We examine the daily activity and performance of a large panel of individual investors in Sweden’s Premium Pension System in the period 2000 to 2010. We find that active investors outperform passive investors, and that there is a causal effect of fund changes on performance. Chosen funds outperform discarded funds over all the horizons we study. This outperformance is most significant for changesmade within an asset class and towards funds with better recent past performance.While activity is beneficial for some individual investors, extreme flows out of mutual funds affect funds’ net asset value negatively for all investors.