Eighty-six diabetic patients with post-treatment painful neuropathy were studied to clarify the clinical characteristics. The mean age of the patients was 46 years and ranged from 19 to 78. The male/female sex ratio was 55/31. Seventy-three patients had NIDDM, 11 had IDDM and 2 had secondary diabetes. The mean duration of diabetes was 7.7years including untreated periods of 5years. At the time glycemic control was started, the mean HbA_1c was 14%(range, 9.2-23%) and the mean BMI was 18.7 (range, 13-30). Several weeks after initiating the therapy, dramatic and severe pain developed in their lower extremities and spread evenly throughout the body, ac companiedby anorexia, insomnia and much greater weight loss. The symptoms subsided during a year of treatment with such drugs as mexiletine, imipramine and fluphenazine. However, diabetic retinopathy developed in 67% of the subjects. The mechanism and pathogenesis of post-treatment painful neuropathy are still unclear but greater caution should be taken in starting glycemic control in diabetic patients with prolonged hyperglycemia and previous neuropathy.