Prior studies have documented that firms' operating performance deteriorates following seasoned equity offerings (SEOs) Previous studies have documented that firms' operating performance deteriorates following seasoned equity offerings (SEOs). Meanwhile, the postissue stock returns of SEO firms are inordinately low relative to various benchmarks of expected returns.1 A popular explanation seems to be managers' timing the market where their decision of SEO is in anticipation of poor future performance. In this paper, I present an overinvestment explanation for poor firm performance after SEOs. Managers' overinvestment of SEO proceeds leads to this poor performance. More specifically, I find that controlling for the differences in industry, investment opportunities, and financial slack, SEO firms still invest more heavily than nonissuing firms and this excess investment is negatively related to postissue operating performance. Further evidence indicates that overinvestment significantly reduces the asset productivity of SEO firms.Why do managers of SEO firms overinvest after equity offerings? Jensen (1986Jensen ( , 1993 argues that managers have various incentives to grow their firm beyond the optimal size. They can enjoy more private benefits by managing a larger firm and their compensation is dependent upon asset growth rather than profitability. Seasoned equity offerings are an effective way to grow firm size. For example, the average SEO proceeds in my sample are 24% of the issuing firm's market value and they are all cash. The probability of overinvestment increases with free cash flow under managers' control.