A study of chronic neurological sequelae resulting from organophosphate pesticide poisoning was conducted. The study group consisted of 128 men, 16 years or older, identified as having been treated for organophosphate poisoning between 1982 and 1990. Of the cases, 83 had documented cholinesterase (ChE) inhibition and were considered to have been definitely poisoned. Thirty six had been hospitalized. The cases were matched to 90 men who had never been exposed to pesticides. The evaluation included a neurological examination, five nerve conduction tests, two tests of vibrotactile sensitivity, evaluation of performance on a neurobehavioral test battery, and measurements of postural sway. The neurobehavioral battery included tests measuring affect, motor speed, sustained visual attention, hand and eye coordination, simple reaction time, coding speed, pattern memory, and serial digit learning. The mean number of days lost from work because of pesticide poisoning (disability days) was 3.8 days. For all cases, the only statistically significant difference from the comparisons occurred for performance on the sustained visual attention test, and the tension and confusion scales on the affect test. When the 83 cases with documented ChE inhibition were considered, finger and toe vibrotactile sensitivity was significantly worse than in the comparisons. When the 36 hospitalized cases were considered, vibrotactile sensitivity and performance on the sustained visual attention and a symbol digit test were significantly worse than for the comparisons. Impaired peroneal nerve conduction velocity, finger vibrotactile sensitivity, and impaired performance on most neurobehavioral tests tended to be associated with increasing numbers of disability days. The authors conclude that no symptomatic neurological impairment has been found in this population of males previously poisoned by organophosphate pesticides. Some evidence of peripheral nerve injury and deficits in central nervous system function has been found.