Initial Class Prospectus | MFS Global Tactical Allocation Portfolio | Initial Class

MFS Global Tactical Allocation Portfolio Summary of Key Information

Investment Objective

The fund’s investment objective is to seek total return.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares of the fund.  If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Annual Fund Operating Expenses	Initial Class Prospectus MFS Global Tactical Allocation Portfolio Initial Class
Management Fee	0.70%
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.06%
Total Annual Fund Operating Expenses	0.76%

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods; your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Although your actual costs will likely be higher or lower, under these assumptions your costs would be:

Expense Example (USD $)	1 YEAR	3 YEARS	5 YEARS	10 YEARS
Initial Class Prospectus MFS Global Tactical Allocation Portfolio Initial Class	78	243	422	942

Portfolio Turnover

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance.  During the most recent fiscal year, the fund’s portfolio turnover rate was 38% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund’s investment adviser) seeks to achieve the fund’s objective by generating returns from a combination of (1) individual security selection of a combination of debt instruments and equity securities and (2) a tactical asset allocation overlay primarily using derivative instruments to manage the fund’s exposure to asset classes, markets and currencies. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.

The fund’s performance may not be correlated with the performance of the asset classes, markets or currencies represented by the individual investments selected by MFS.

Individual Security Selection: In selecting direct investments for the fund, MFS normally invests the fund’s assets in a combination of debt instruments and equity securities. Debt instruments include corporate bonds, U.S. Government securities, foreign government securities, asset-backed securities, municipal instruments, inflation-adjusted bonds, and other obligations to repay money borrowed. Equity securities include common stocks, preferred stocks, securities convertible into stocks, equity interests in real estate investment trusts (REITs), and depositary receipts for those securities. MFS generally invests approximately 65% of the fund’s assets in debt instruments and cash and/or cash equivalents and approximately 35% of the fund’s assets in equity securities, of which approximately 25% are generally non-U.S. dollar denominated investments. These allocations may vary significantly from time to time.

MFS may invest the fund’s assets in U.S. and foreign securities, including emerging market securities.

MFS may invest a large percentage of the fund’s assets in issuers in a single country, a small number of countries, or a particular geographic region.

Of the fund’s investments in debt instruments, MFS generally invests substantially all of these investments in investment grade debt instruments.

While MFS may invest the fund’s assets in companies of any size, MFS generally focuses on companies with large capitalizations.

MFS focuses on investing the fund’s assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies).

While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives as part of its individual security selection process, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments.

A team of investment professionals selects investments for the fund. MFS allocates the fund’s assets to investment professionals by investment strategy. MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers and instruments. Quantitative models that systematically evaluate issuers and instruments may also be considered.

Tactical Asset Allocation Overlay:  MFS employs a top-down tactical asset allocation process to adjust the fund’s exposure to asset classes, markets, and currencies based on its assessment of the relative attractiveness of such asset classes, markets, and currencies. MFS manages the fund’s exposure to asset classes, markets and currencies primarily through the use of derivative instruments based on its proprietary quantitative models.

In managing the tactical overlay, MFS may increase or decrease the fund’s exposure to asset classes, markets and/or currencies resulting from MFS’ individual security selection based on MFS’ assessment of the risk/return potential of such asset classes, markets and/or currencies.  The fund’s exposure to the equity security asset class after taking into account the tactical overlay may generally range from 0% to approximately 70% of the fund’s assets.  Correspondingly, the fund’s exposure to the debt instrument asset class after taking into account the tactical overlay may at times be as high as 100%. The fund’s exposure to non-U.S. dollar denominated investments after taking into account the tactical overlay may generally range from 0% to approximately 50% of the fund’s assets. MFS may also expose the fund to asset classes, markets and/or currencies in which its individual security selection has resulted in no or little exposure (e.g., commodities).

MFS may adjust the fund’s net exposure to asset classes, markets and/or currencies by taking net short positions in an asset class, market or currency if MFS believes the risk/return potential of such asset class, market or currency is unattractive.  Alternatively, MFS may cause the fund to take net long positions in an asset class, market or currency if MFS believes such asset class, market or currency appears attractive.

MFS expects to also use derivatives to seek to limit the fund’s exposure to certain extreme market events if the fund’s exposure to the equity security asset class after taking into account the tactical overlay is greater than 35% of the fund’s assets.

MFS’ tactical asset allocation process for the fund will typically make extensive use of derivatives.

Principal Risks

As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Investment Selection and Allocation Risk:  MFS’ investment analysis, its selection of investments, its assessment of the risk/return potential of asset classes, markets and currencies, and its adjustments to the fund’s exposure to asset classes, markets, and currencies may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.

Investment Strategy Risk:  The fund’s strategy to manage its exposure to asset classes, markets, and currencies may not produce the intended results. In addition, the strategies MFS may implement to limit the fund’s exposure to certain extreme market events may not work as intended, and the costs associated with such strategies will reduce the fund’s returns.

Interest Rate Risk: The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.

Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.

Stock Market/Company Risk: Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.

Derivatives Risk: Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost.  Derivatives can involve leverage.

Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets.

Currency Risk:  The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, and other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency.

Geographic Concentration Risk: The fund’s performance could be closely tied to the market, currency, economic, political, regulatory, geopolitical, and other conditions in the countries or regions in which the fund invests and could be more volatile than the performance of more geographically-diversified funds.

Prepayment/Extension Risk: Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.

Inflation-Adjusted Debt Instruments Risk: Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.

Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market.

Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.

Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.

Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction.

Liquidity Risk: It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.

Performance Information

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.

Performance information prior to February 8, 2010, reflects time periods when the fund (i) had a policy of investing between 40% and 75% of its assets in equity securities and at least 25% of its assets in fixed income senior securities and (ii) did not employ a tactical asset allocation overlay. The fund’s investment policies and strategies changed effective February 8, 2010. The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the three-month period ended March 31, 2013 was 2.49%. During the period(s) shown in the bar chart, the highest quarterly return was 12.38% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (9.70)% (for the calendar quarter ended March 31, 2009).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2012)

Average Annual Returns Initial Class Prospectus MFS Global Tactical Allocation Portfolio	Label	Average Annual Returns, 1 Year		Average Annual Returns, 5 Years		Average Annual Returns, 10 Years
Initial Class	Initial Class Shares	9.56%		2.72%		8.11%
Initial Class Barclays Global Aggregate Bond Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays Global Aggregate Bond Index	4.32%		5.44%		5.98%
Initial Class Barclays Global Aggregate Bond Index Hedged	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays Global Aggregate Bond Index Hedged	5.72%		5.28%		4.76%
Initial Class MFS Global Tactical Allocation Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Global Tactical Allocation Blended Index	9.44%	[1]	3.72%	[1]	6.38%	[1]
Initial Class MSCI World Index (gross div)	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MSCI World Index (gross div)	16.54%		(0.60%)		8.08%

[1] As of December 31, 2012, the MFS Global Tactical Allocation Blended Index (the "Blended Index") consisted of the following indices and weightings: 35% MSCI World Index (gross div), 54% Barclays Global Aggregate Bond Index Hedged, and 11% Barclays Global Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.