Three patients with diabetes are described. Two patients had a mild, well controlled, hyperglycemic syndrome; five years after its detection signs of nephropathy and retinopathy appeared. Both died of renal failure ten years after detection of diabetes. The third patient died at the age of forty-seven of recurrent myocardial infarction. During her terminal hospitalization uremia and hyperglycemia were first discovered. Histologic findings in postmortem material were identical in all three cases. Heavy deposits of pediodic acid-Schiff-positive, colloidal iron and Congo red negative material were found in the blood vessels of virtually all organs examined. The blood vessels involved ranged from capillaries, venules, arterioles to arteries of large size. In some areas the material was seen also in connective tissue outside of blood vessels. Electronmicroscopic examination revealed that the PAS-positive material was composed of fibrils, approximately 100Å wide. These findings indicate the presence of a systemic disease of connective tissue in our cases, resembling systemic amyloidosis in extent, location and nature. We suggest the name, diabetic fibrillosis.