mksinitialprosp.htm

Before you invest, you may want to review the fund’s prospectus, which contains more information about the fund and its risks. You can find the fund’s prospectus and other information about the fund, including the fund’s statement of additional information, online at insurancefunds.mfs.com. You can also get this information at no cost by calling 1-800-225-2606 or by sending an e-mail request to orderliterature@mfs.com. The fund’s prospectus and statement of additional information, both dated April 30, 2011, as may be supplemented from time to time, are incorporated by reference into this Summary Prospectus.

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 investment vehicle through which an investment in the fund is made were included, your expenses would be higher.


Management Fee	0.50%
Distribution and/or Service (12b-1) Fees	None
Other Expenses	0.09%
Total Annual Fund Operating Expenses	0.59%
Fee Reductions and/or Expense Reimbursements1	(0.02)%
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	0.57%

MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.57% of the fund's average daily net assets annually for Initial Class shares. This written agreement will continue until modified by MFS for any reason, but such agreement will continue until April 30, 2012.

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.

MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the fund’s assets in U.S. dollar-denominated money market instruments and repurchase agreements. Money market instruments include bank certificates of deposit and other bank obligations of U.S. and foreign banks; notes, commercial paper, and asset-backed securities of U.S. and foreign issuers; U.S. and foreign government securities; and municipal instruments.

In buying and selling investments for the fund, MFS seeks to comply with Securities and Exchange Commission rules for money market funds regarding credit quality, diversification, liquidity, and maturity. MFS stresses maintaining a stable $1.00 share price, liquidity, and income.

The Board of Trustees has approved submitting the following concentration policy to shareholders of the fund for approval at a special meeting of shareholders expected to be held in December 2011:

Although the fund seeks to preserve the value of your investment at $1.00 per share, the fund may not achieve its objective and 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.

Interest Rate, Credit, and Liquidity Risk: Although MFS seeks to maintain a stable $1.00 share price for the fund, there is no guarantee that it will be able to do so. A major increase in interest rates or a decline in the credit quality of an issuer or entity providing credit support, an inactive trading market for money market instruments, or adverse market, economic, political, regulatory, geopolitical, or other conditions could cause the fund’s share price to decrease to below $1.00.

Foreign Exposure Risk: Exposure to foreign markets can involve increased risks due to adverse market, economic, political, regulatory, geopolitical, or other conditions.

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.

Investment Selection Risk: The MFS analysis of an investment can be incorrect and 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.

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.

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.

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.

The total return for the three-month period ended March 31, 2011, was 0.00%. During the period(s) shown in the bar chart, the highest quarterly return was 1.33% (for the calendar quarter ended March 31, 2001) and the lowest quarterly return was 0.00% (for the calendar quarter ended March 31, 2009, June 30, 2009, September 30, 2009, December 31, 2009, March 31, 2010, June 30, 2010, September 30, 2010, and December 31, 2010).

Because shares of the fund are offered to insurance company separate accounts, qualified retirement plans and pension plans, and other eligible investors, you should consult with the insurance company that issued your contract, plan sponsor, or other eligible investor through which your investment in the fund is made to understand the tax treatment of your investment.

If you purchase the fund through an insurance company, plan sponsor, broker-dealer, or other financial intermediary, the fund, MFS, and its affiliates may make payments to insurance companies, plan sponsors, other financial intermediaries, and all of their affiliates for distribution and/or other services. These payments may create a conflict of interest for the insurance company, plan sponsor, or other financial intermediary to include the fund as an investment option in their product or to recommend the fund over another investment option. Ask your financial intermediary, insurance company, or plan sponsor, or visit your financial intermediary's or insurance company's Web site, for more information.

CLASS	TICKER SYMBOL
Initial Class	N/A

	1 YEAR	3 YEARS	5 YEARS	10 YEARS
Initial Class Shares	$58	$187	$327	$736

Share Class	1 YEAR	5 YEARS	10 YEARS
Initial Class Shares	0.00%	2.27%	2.05%