We treated a diabetic patient with familial multiple endocrine neoplasia type 1 (MEN 1) who had undergone total pancreatoduodenectomy. The patient received insulin and showed signs of symptomatic primary hyperparathyroidism (PHPT). The insulin requirement to control blood glucose before and after parathyroidectomy was compared by using an artificial pancreas. The insulin infusion rate during the day and at night was reduced to about one-third and half, respectively, after parathyroidectomy with autotransplantation of parathyroid tissues into the forearm. The daily insulin dose was reduced from 36 units to 14 units 2 weeks after surgery, and glycemic control showed further improvement 2 months after surgery with the same dose of insulin for up to 6 months. These observations suggest that insulin sensitivity increases after surgical correction of PHPT.