This paper examines whether insiders use private information to time the exercises of their executive stock options. Before May 1991, insiders had to hold the stock acquired through option exercise for six months. Exercises from that regime precede signi ̄cantly positive abnormal stock performance, suggesting the use of inside information to time exercises. By contrast, we ̄nd little evidence of such timing since insiders have been able to sell acquired shares immediately. Now, such timing should show up as negative abnormal stock returns after option exercise. However, we ̄nd negative stock performance only after exercises by top managers at small ̄rms.