To determine the risk of transmission of human T-cell lymphotropic virus Type III/lymphadenopathy-associated virus (HTLV-III/LAV) to close but nonsexual contacts of patients with the acquired immunodeficiency syndrome (AIDS), we studied the nonsexual household contacts of patients with AIDS or the AIDS-related complex with oral candidiasis. Detailed interviews, physical examinations, and tests for serum antibody to HTLV-III/LAV were performed on 101 household contacts of 39 AIDS patients (68 children and 33 adults), all of whom had lived in the same household with an index patient for at least three months. These contacts had shared household items and facilities and had close personal interaction with the patient for a median of 22 months (range, 3 to 48) during the period of presumed infectivity. Only 1 of 101 household contacts--a five-year-old child--had evidence of infection with the virus, which had probably been acquired perinatally rather than through horizontal transmission. This study indicates that household contacts who are not sexual partners of, or born to, patients with AIDS are at minimal or no risk of infection with HTLV-III/LAV.