Using a unique new dataset linking administrative data on investment performance and financial knowledge, we examine whether investors who are more financially knowledgeable earn more on their retirement plan investments, compared to their less sophisticated counterparts. We find that risk-adjusted annual expected returns are 130 basis points higher for the most financially knowledgeable employees, and those scoring higher on our Financial Knowledge Index have slightly more volatile portfolios while they do no better diversifying their portfolios than their peers. Overall, financial knowledge does appear to help people invest more profitably; this may provide a rationale for efforts to enhance financial knowledge in the population at large.