To evaluate the latent neurological effects of organophosphate pesticide poisoning, this epidemiologic study examined 100 matched-pairs of individuals with previous acute organophosphate pesticide poisoning and nonpoisoned controls. No significant difference between poisoned subjects and controls was found on audiometric tests, ophthalmic tests, electroencephalograms, or the clinical serum and blood chemistry evaluations. Of the more than 50 scores from the neurological examination, abnormalities were demonstrated among the cases only on measures of memory, abstraction, and mood, and on one test of motor reflexes. Differences between the two cohorts were much more apparent in the neuropsychological tests. The differences occurred on tests of widely varying abilities including intellectual functioning, academic skills, abstraction and flexibility of thinking, and simple motor skills. Twice as many cases as controls (24 vs. 12) had Halstead-Reitan Battery summary scores in the range characteristic of individuals with cerebral damage or dysfunction. Results from the Minnesota Multiphasic Personality Inventory and the Patient's and Relative's Assessment of Patient Functioning Inventories also revealed greater distress and complaints of disability for the poisoned subjects.