Diabetes mellitus is a major cause of morbidity and mortality, and it is a major risk factor for early onset of coronary heart disease. Complications of diabetes are retinopathy, nephropathy, and peripheral neuropathy. Currently, treatment involves diet modification, weight reduction, exercise, oral medications, and insulin. In recent years, important advances have been made into the pathogenesis of diabetes that affect the cardiovascular, renal, and nervous systems; vision; and the lower extremities, especially the feet. The progression of diabetic retinopathy and nephropathy can be slowed or prevented with tight glucose and blood pressure control. Neuropathy remains a major problem causing significant impairment. Ongoing clinical trials and testing of various medications to determine their effectiveness in treating the complications of diabetes have met with some success, but there still is much to learn about this disease.