Abstract: Some eleven million 401(k) plan participants take a concentrated equity position in their retirement savings account, investing more than 20% of the balance in their employer's common stock. Yet investing in the stock of one's employer is a risky investment on two counts: single securities are riskier than diversified portfolios (such as mutual funds), and the employee's human capital is typically positively correlated with the performance of the company. In the worst-case scenario, illustrated by the Enron bankruptcy, workers can lose their jobs and much of their retirement wealth simultaneously. For workers who expect to work for the company for many years, a dollar of company stock can be valued at less than 50 cents to the worker after accounting for the risks. But employees still invest voluntarily in their employers' stock, and many employers insist on making matching contributions in stock, despite the fact that a dollar of investment or contribution may be worth only 50 cents on the dollar. How can competitive labor markets sustain a situation in which employers and employees make such a fundamental miscalculation? We provide evidence that employees underestimate the risk of owning company stock, while employers overestimate the benefits associated with employee stock ownership relative to its costs. This evidence provides strong reasons to consider legal reforms in this domain. We make suggestions that would increase employees' freedom of choice and improve their welfare, but without imposing significant costs on well-meaning but ill-informed employers.