We studied HIV prevalence in couples in Chennai, India. In 56% both partners were infected. Among discordant couples, 35 men and seven women were infected. Heterosexual intercourse is the primary risk factor. Concordance was related to sex with commercial sex workers for men and to genital ulcer disease for women. Median CD4 count was 97 cells/mm(3) among concordant men, 222 cells/mm(3) among discordant men. Condom use increased, and frequency of sexual intercourse decreased, among all couples after HIV diagnosis.