<p>High temperatures can have a negative effect on workplace safety for various reasons. Discomfort and reduced concentration caused by heat can lead to workers making mistakes and injuring themselves. Discomfort can also be an incentive for workers to report an injury that they would not have reported in the absence of heat. We investigate how temperature affects injuries of professional tennis players in outdoor singles matches. We find that injury rates increase with ambient temperatures for men, whereas for women, high temperatures have no effect on injury rates. Among male tennis players, there is some heterogeneity in the temperature effects, influenced by incentives. Specifically, when a male player is losing at the beginning of a crucial second (third) set in best-of-three (best-of-five) matches, the temperature effect is much larger than when he is winning.</p>