Conventional wisdom suggests that insiders buy shares on positive, and sell on negative, information. Under regulations of insider trading, however, insiders keep silent while possessing extreme information. We find that this phenomenon of insider silence is systematically related to a broad set of anomalies, particularly in the short legs. Specifically, among firms in the short legs, those whose insiders kept silent in the past experience significant negative future returns, which are even lower than when insiders net sold. On average, insider silence accounts for 64% of the short-leg abnormal returns. Our paper provides quantitative evidence of mispricing for return anomalies.