Seventy-six homosexual or bisexual men underwent two cranial MRI studies at a mean interval of 13 months; 23 were HIV seronegative, 41 seropositive but asymptomatic (Center for Disease Control (CDC) groups II/III), and 12 had AIDS related complex (ARC)/AIDS (CDC group IV). Agreement between two neuroradiologists was rated as very good for assessment of enlargement of ventricles and good for widening of cerebral sulci and the presence of focal lesions. For assessment of serial studies, the agreement was moderate. The prevalence of cerebral atrophy and focal white matter lesions was no higher in the asymptomatic patients (CDC group II/III) than in appropriate seronegative controls. Some patients with ARC/AIDS showed evidence of developing cerebral atrophy during the study period when serial scans were compared. The imaging evidence supports the other data obtained from this cohort, which suggest that no significant CNS involvement occurs in HIV infection before the development of ARC/AIDS.