ABSTRACT.AIDS dementia, and the more subtle forms of cognitive dysfunction which may precede it, are important but poorly understood aspects of human immunodeficiency virus (HIV) infection. Event related potential (ERP) data have been obtained from 83 HIV+ subjects at a first, 47 at a second, and 29 at a third examination at six month intervals. Significant increases in P3 latency in both asymptomatic and symptomatic groups were found by repeated measures testing. N2 latencies were significantly prolonged in both the asymptomatic and symptomatic groups relative to control values but did not increase with time. Earlier (N1 and P2) components were not increased although a trend was present for an increase in P2 over time. A significant difference between asymptomatic and symptomatic groups was not defined for any ERP component latency.The N2 and the P3 components of the P3 event related potential are frequently abnormal in HIV+ subjects with the P3 latency showing increasing abnormality over time. There has been insufficient evidence of neurological dysfunction in the patient group under study to permit estimation of the clinical significance of these ERP changes in AIDS.