ObjectiveTo examine changes in sexual activity and unprotected sexual intercourse among HIV-infected patients before and after the initiation of protease inhibitor therapy.DesignAn analysis of data from the SEROCO Study, a French prospective cohort.MethodsAll 191 patients who initiated protease inhibitor therapy after 1 January 1996, who were interviewed within one year before the initiation of therapy (Time 1), and who had at least 6 months of follow-up after therapy initiation (Time 2) were included. Patients provided information about sex partner characteristics and unprotected sexual intercourse.ResultsEighty-one (42%) were gay or bisexual men, 46 (24%) were heterosexual men, and 64 (34%) were women. No significant increases were found in either the number of patients reporting anal or vaginal sex or the number reporting unprotected sexual intercourse after protease inhibitor initiation. However, in matched pair analysis, gay or bisexual men were three times more likely to report having had unprotected sexual intercourse with partners who were of HIV-negative or unknown serostatus after protease inhibitor initiation [relative risk (RR) = 3.0, 95% confidence interval (CI) = 1.2–7.6]. Non-significant decreases in unprotected sexual intercourse among both heterosexual men and women were also observed. No relationship between plasma viral load after protease inhibitor initiation and unprotected sexual intercourse was found in these data.ConclusionsA relapse in sex risk practices among some HIV-infected gay or bisexual men cannot be ruled out and requires both continued monitoring and immediate secondary preventative intervention.