Individuals infected with the acquired immunodeficiency syndrome (AIDS) are at risk for developing cognitive impairment. The extent to which the impairment represents the results of a single factor accounting for a wide degree of cognitive dysfunction, or is the result of the combined effects of multiple factors, has not been determined. In the present study, we analyzed data from 134 patients with AIDS and 105 HIV− controls using a recently developed analytical procedure. The results revealed that, by and large, the test variables shared a significant amount of variance related to disease status. Hence the AIDS-related influences on cognition are shared and thus cannot be considered independent. Two tests, Digit Symbol Substitution, and the primacy measure of verbal free recall, had a direct relationship with the group variable (AIDS vs. controls). These results suggest that a single factor is sufficient to account for a large proportion of the AIDS-related variance on a wide variety of neuropsychological tests. (JINS, 1999, 5, 41–47.)