The prevalence of symptomatic sensorimotor polyneuropathy has been determined in a population of 382 insulin-treated diabetic subjects aged 15-59 yr. Forty-one subjects (10.7%) were found to have diabetic neuropathy, according to strict diagnostic criteria that required the presence of symptoms and signs of nerve dysfunction in the absence of peripheral vascular disease. There was a significant correlation between glycosylated hemoglobin levels and motor conduction velocity in the median and peroneal nerves in all subjects. This finding further emphasizes the importance of metabolic factors related to hyperglycemia in the impaired nerve function seen in diabetic patients.