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MFS® Blended Research® Small Cap Equity Portfolio

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Supplement [Text Block]

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SUPPLEMENT TO PROSPECTUS
The date of this supplement is August 20, 2015.

MFS® Blended Research® Small Cap Equity Portfolio
Initial Class & Service Class Shares

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MFS® Blended Research® Small Cap Equity Portfolio

Strategy Narrative [Text Block]

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Effective August 11, 2015, the fifth paragraph in sub-section entitled "Principal Investment Strategies" under the main heading "Summary of Key Information" is restated in its entirety as follows:

MFS uses a bottom-up approach to buying and selling investments for the fund. Investments are selected primarily based on blending fundamental and quantitative research. MFS uses fundamental analysis of individual issuers to create a fundamental rating for an issuer.  MFS uses quantitative models to create a quantitative rating for an issuer. MFS then constructs the portfolio considering the blended rating from combining the fundamental rating and the quantitative rating, as well as issuer, industry, and sector weightings, market capitalization, measures of expected volatility of the fund's return (e.g., predicted beta and predicted tracking error), and other factors, with a goal of constructing a portfolio that over time has a consistent level of active risk compared to the Russell 2000. Active risk is the risk resulting from investment selection rather than market risk.

Risk Narrative [Text Block]

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Effective August 11, 2015, the fourth paragraph in the sub-section entitled "Principal Risks" under the main heading "Summary of Key Information" is restated in its entirety as follows:

Investment Strategy Risk: The fund's strategy to blend fundamental and quantitative research and to have a consistent level of active risk over time may not produce the intended results. In addition, MFS fundamental research is not available for all issuers.