Introduction - The interaction between HIV and sexually transmitted infections (STIs) is complex. STIs facilitate HIV transmission and vice versa. The objective of this article is to describe the prevalence of HIV seropositivity among patients for whom a diagnosis of an STI (syphilis, gonorrhea, and lymphogranuloma venereum [LGV] of the rectum) was reported to the national surveillance network RésIST between 2000 and 2007. Method - STI surveillance is voluntary in metropolitan France and the French overseas departments. It relies on STI Information, Screening, and Diagnosis Centers (Ciddist), hospital clinics, and private medical practices. Cases are defined according to clinical and laboratory criteria. Clinical data from the questionnaire are documented by the clinician and supplemented by a self-administered questionnaire on sexual behavior during the 12 months preceding the STI diagnosis. The anonymous questionnaires are sent by the physician to the French Institute for Public Health Surveillance. Results - During the study period, 2,892 cases of syphilis, 653 cases of gonorrhea, and 567 cases of LGV were reported. HIV prevalence was 16%, 45%, and 90% among patients with gonorrhea, syphilis, and LGV, respectively. All LGV-positive patients were homosexual. For gonorrhea and syphilis, the prevalence of HIV seropositivity varied by sexual orientation; it was higher among gay and bisexual men (23% and 51%, respectively) compared to heterosexual men (3% and 16%) and heterosexual women (3% and 6%). Among HIV-positive patients, the proportion of patients learning of their HIV status at the time of STI diagnosis was high: 18% for patients with gonorrhea and 12% for patients with syphilis. Conclusion - The prevalence of HIV infection is high among patients diagnosed with STIs (syphilis, gonorrhea, and LGV), and a significant proportion of patients learn of their HIV status at the time of STI diagnosis. Continued efforts are needed to promote comprehensive primary and secondary prevention targeting all STIs (HIV and others). (R.A.)