The objective of this study was to assess the prevalence and pattern of neuropsychological impairment in cohorts of human immunodeficiency virus (HIV)-infected individuals across pre- and post-HAART (highly active antiretroviral therapy) eras. Two cohorts of HIV-infected individuals attending tertiary referral hospital outpatient clinics were studied. The cohorts represented two eras of antiretroviral medication: monotherapy (n = 51) and HAART (n = 90). Each was compared in nine neuropsychological domains in regard to the prevalence as well as pattern of neuropsychological impairment. Because the authors intended to characterize the prevalence and pattern of neuropsychological deficits in nondemented advanced HIV-infected individuals, patients with a current diagnosis of acquired immunodeficiency syndrome (AIDS) dementia complex were not included. The prevalence of impairment was not significantly different across pre-HAART and HAART eras using a standard criterion to define impairment: -2 SD in two neuropsychological measures (41.1%/38.8%). Prevalence of deficits was not significantly reduced in patients with undetectable plasma viral load. The pattern of neuropsychological impairment was different across pre-HAART and HAART eras, with an improvement in attention, verbal fluency, visuoconstruction deficits, but a deterioration in learning efficiency and complex attention. This change remained even in patients with an undetectable plasma viral load, although the severity was partially diminished. Neuropsychological deficits remain common in the HAART era, essentially uninfluenced by HAART. The finding that some neuropsychological functions are improving while other are deteriorating indicates that these deficits do not reflect "burnt out" damage but rather that there is an active intracerebral process occurring, the nature of which is still to be determined.