Reports available on the extent and incidence of cognitive deficits in human immunodeficiency virus (HIV-1) patients are variable. To assess the influence of drug abuse and psychiatric symptoms on the extent of the cognitive deficit, we examined 42 drug-addicted HIV-1 patients and compared them with a group of seronegative drug addicts (n = 31) as well as with a group of healthy controls (n = 50), using a psychometric test battery and standardized psychiatric scales. We found no significant difference in the extent and incidence of cognitive deficits in the group of HIV-1 patients as compared with the seronegative drug addicts. Both groups, however, differed from the normal population group. Remarkable depressive symptoms were found in the HIV-1 infected patient group. We assume that long-term drug abuse contributes markedly to the cognitive deficit of HIV-1 patients, which is further influenced by depressive symptoms.