Insider trading potentially reveals proprietary information, allowing rivals to compete more effectively against the insiders' firm. This paper examines whether proprietary costs are associated with insiders' trading decisions and the profitability of their trades. Using a variety of approaches to identify proprietary information risk, I find proprietary costs significantly deter insiders' trading activities. The deterrence effect is more pronounced when insider trading is likely to be more informative to rivals. Specifically, trades by top executives, non-routine trades, and trades at low complexity firms are curbed to a greater extent by proprietary costs. Examining the mechanisms of this deterrence effect, I find firms with higher proprietary costs are more likely to impose insider trading restrictions, and insiders' trading decisions are more sensitive to proprietary costs when they have higher share ownership of the company. These results suggest insiders reduce trading activities not only due to firm policies, but also due to incentive alignment. Finally, when insiders trade despite higher proprietary costs, they earn significantly higher abnormal profits from their purchase transactions. Overall, this study suggests product market considerations are an important factor associated with insiders' trading decisions and profitability of their trades. These findings are likely to be of interest to regulators and corporate boards in setting insider trading policies, and help investors make investment decisions using insider trading signals.