Crescents, defined as any proliferative or fibrous space occupying reaction of the parietal layer of Bowman's capsule, occur as a regular and integral feature of the glomerular changes of diabetes mellitus. The frequency of crescents and adhesions to the capsule increases with increasing total severity of diabetic glomerular and vascular disease in glomeruli with mild-moderate diffuse glomerulosclerosis (GS), severe diffuse GS, and nodular GA. The high frequency (greater than 90 per cent) of crescents and adhesions in glomeruli with exudative lesions is unrelated to over-all severity of diabetic renal disease. The 8.73 per cent of glomeruli with exudative lesions had 45 per cent of the total crescents observed. The mechanism of crescent formation in diabetes is probably similar to the proposed pathogenesis of crescents in other renal diseases. The underlying injury in the glomerular capillaries in diabetes is mainly the "exudative lesion." The percentage of diabetic glomeruli with crescents correlated better with blood urea nitrogen and creatinine that did the percentage of end stage glomeruli (a measure of severity of vascular disease), the percentage of diabetic glomeruli with severe diffuse GS, the percentage of diabetic glomeruli with nodular GS, or the percentage of diabetic glomeruli with exudative lesions. The percentage of diabetic glomeruli with crescents correlated better with severity of vascular disease than did any of the other diabetic glomerular changes. No correlation existed between incidence of crescents and "capsular drops."