Previous studies of human immuno-deficiency virus-related neurologic disease have been either retrospective or have included mostly homosexual patients. We sought to determine (1) the true prevalence of neurologic abnormalities in patients with acquired immunodeficiency syndrome or lymphadenopathy acquired immunodeficiency-related complex, and (2) whether differences in prevalence or type of neurological abnormality exist between parenteral drug abusers and non-parenteral drug abusers. We prospectively evaluated 190 adult inpatients with either acquired immunodeficiency syndrome (129) or lymphadenopathy acquired immunodeficiency-related complex (61); 151 (80%) were parenteral drug abusers, and 172 patients (91%) had neurologic symptoms or signs. There was no significant difference in prevalence of neurologic disease between parenteral drug abusers and non-parenteral drug abusers, or between patients with acquired immunodeficiency syndrome and those with lymphadenopathy acquired immunodeficiency-related complex. The prevalence of neurologic symptoms in these patients with lymphadenopathy acquired immunodeficiency-related complex and acquired immunodeficiency syndrome is the highest reported to date and appears to reflect the prospective nature of the study.