A 14-year-old boy presented with Type I diabetes mellitus and subsequently developed pancreatic exocrine insufficiency and systemic sclerosis (SSc). His diabetes had been diagnosed when he was about 5 years old, after the onset of ketoacidosis. Insulin treatment was provided from then until the time he was treated in our department. Exocrine pancreatic insufficiency, which occurred at age 9, was treated with pancreatic extracts. Cystic fibrosis was excluded after a chloride sweat test. The diagnosis of SSc was confirmed at age 14 on the basis of skin sclerosis, sclerodactyly and oesophageal and pulmonary involvement and then at age 18 by the occurrence of Raynaud's disease. Thus, this patient demonstrated a rare and previously unreported association of Type I diabetes mellitus and systemic scleroderma. Limited joint mobility and skin abnormalities are frequent in childhood diabetes mellitus but should not be misdiagnosed as systemic scleroderma.