Despite the high prevalence of diabetes mellitus in patients with chronic pancreatitis, few studies of pancreatic diabetes have been reported. We investigated 154 patients with chronic pancreatitis, of whom 50% were diabetics, with special reference to the features and clinical course of pancreatic diabetes. We arrived to clarify the features of pancreatic diabetes by comparing pancreatic exocrine function in 112 patients with primary diabetes with findings in a separate group of 80 patients with chronic pancreatitis. Pancreatic diabetes is proposed as a type of diabetes in which exocrine pancreatic function is markedly decreased. Progressive and fatal angiopathies were found in patients with pancreatic diabetes after a long duration of diabetes. The present investigation suggests that treatment of malnutrition is necessary in patients with pancreatic diabetes and that control of blood glucose is often difficult in these patients because of the high incidence of insulin-induced hypoglycemic episodes.