A 24-year-old woman developed the acquired immunodeficiency syndrome with lymphadenopathy, oral candidiasis, and Kaposi's sarcoma. Her only known risk factor for the syndrome was sexual contact with an asymptomatic Haitian man. The woman had serologic evidence for infection with human T-cell lymphotropic virus type III, and this virus was recovered from the saliva of her sexual partner. Epidemiologic and virologic studies of the cases of such patients provide further evidence of a primary pathogenetic role for this retrovirus in the acquired immunodeficiency syndrome.