A 36-year-old woman with a 26-year history of insulin-dependent diabetes mellitus developed chronic renal failure in 1974 and was started on dialysis. She received a kidney transplant from her HLA-identical brother. Her HLA typing showed the following antigens: A1, A28, B8, B12 (44), BW4, BW6 DR3, and DR4. Nephrectomy performed prior to transplantation showed advanced diffuse diabetic glomerulosclerosis. Her postoperative course was relatively uncomplicated, but within the next seven years she gradually developed symptoms of deteriorating renal function and hypertension. Two years later, a renal arteriogram showed 90% stenosis of the main renal artery. Biopsy of the kidney was obtained during surgical repair of this lesion and showed diffuse nodular diabetic glomerulosclerosis. Since the B8/DR3 form of diabetes is reported to have a predilection for diabetic microangiopathy and vascular complications, we are speculating that the patient's antigenic composition might have enhanced the recurrence of the diabetic lesions in the transplanted kidney.