Detailed neuropsychological testing was performed on 133 human immunodeficiency virus (HIV) seropositive (SP) and 77 HIV seronegative (SN) individuals, 86 % with early stage HIV infection in Nigeria, to determine the frequency of HIV-related neurocognitive impairment among the HIV-infected group. The tests were administered to assess the following seven ability domains: speed of information processing, attention/working memory, executive functioning, learning, memory, verbal fluency, and motor function motor. Demographically corrected individual test scores and scores for each domain or reflecting a global deficit (a global deficit score, or GDS) were compared for the SP and SN groups. SP participants were older, had fewer years of education, were more likely to be married, differed in ethnicity, and had higher depression scores than SN individuals. Within the seven ability domains, SP performed worse than SN with respect to speed of information processing, executive function, learning, memory, and verbal fluency and also on the global measure. SP were also more frequently impaired on tests of SIP, and there was a borderline increase in the frequency of global impairment. On the individual tests, SP performed worse than SN on four tests that assessed learning, verbal fluency, memory, and motor function (the Timed Gait). SP subjects, however, performed better than SN on the Finger-tapping test, also a motor task. Performance by SP subjects was not associated on the timed gait which showed a borderline statistically significant correlation with CD4 counts. However, there were significant correlations between viral load measurements and individual tests of speed of information processing, executive function, learning, and verbal fluency and with overall executive function and a borderline correlation with the GDS. Depression scores for SP were associated with impairment on only a single test of executive function. These results demonstrate the ability of these assessments to identify areas of impairment that may be specifically linked to a history of HIV infection among individuals in Nigeria. Confirmation of these findings awaits analyses using data from a larger number of control subjects.