AIDS treatment provides enormous mortality benefits to infected individuals but because it immunologically insulates people from more risk-taking, it could, in theory, stir perverse behavioral responses. Therefore, the response of sexual behavior to AIDS treatment in Africa is an important input to predicting the path of the epidemic. Existing estimates from observational studies suggest limited behavioral response, but they fail to take into account possible differences across individuals seeking treatment. Using an encouragement design field experiment conducted in South Africa, I estimate behavioral responses subsequent to AIDS treatment. I find moderate negative responses to treatment for HIV+  individuals and mixed results for HIV-  individuals. Negative behavior response is stronger among males and among individuals who have been recently infected.