OBJECTIVE: To assess whether male circumcision of the primary sex partner is associated with women's risk of HIV. DESIGN: Data were analyzed from 4417 Ugandan and Zimbabwean women participating in a prospective study of hormonal contraception and HIV acquisition. Most were recruited from family planning clinics; some in Uganda were referred from higher-risk settings such as sexually transmitted disease clinics. METHODS: Using Cox proportional hazards models, time to HIV acquisition was compared for women with circumcised or uncircumcised primary partners. Possible misclassification of male circumcision was assessed using sensitivity analysis. RESULTS: At baseline, 74% reported uncircumcised primary partners, 22% had circumcised partners ...