The authors conducted a population-based study to attempt to estimate the effect of human immunodeficiency virus type 1 (HIV-1) seropositivity on Armed Services Vocational Aptitude Battery test scores in otherwise healthy individuals with early HIV-1 infection. The Armed Services Vocational Aptitude Battery is a 10-test written multiple aptitude battery administered to all civilian applicants for military enlistment prior to serologic screening for HIV-1 antibodies. A total of 975,489 induction testing records containing both Armed Services Vocational Aptitude Battery and HIV-1 results from October 1985 through March 1987 were examined. An analysis data set (n = 7,698) was constructed by choosing five controls for each of the 1,283 HIV-1-positive cases, matched on five-digit ZIP code, and a multiple linear regression analysis was performed to control for demographic and other factors that might influence test scores. Years of education was the strongest predictor of test scores, raising an applicant's score on a composite test nearly 0.16 standard deviation per year. The HIV-1-positive effect on the composite score was -0.09 standard deviation (99% confidence interval -0.17 to -0.02). Separate regressions on each component test within the battery showed HIV-1 effects between -0.39 and +0.06 standard deviation. The two Armed Services Vocational Aptitude Battery component tests felt a priori to be the most sensitive to HIV-1-positive status showed the least decrease with seropositivity. Much of the variability in test scores was not predicted by either HIV-1 serostatus or the demographic and other factors included in the model. There appeared to be little evidence of a strong HIV-1 effect.