The decision for simultaneous pancreas-kidney (SPK) versus kidney transplant alone (KTA) in diabetic patients with renal failure depends on the potential risks and benefits for each procedure. The purpose of this study was to compare the morbidity, mortality, and renal allograft survival in diabetic patients who underwent SPK versus KTA, and to discern the added risks associated with pancreas transplantation. Between 7/1/86 and 9/30/90, 69 primary cadaver SPK and 59 primary cadaver KTA were performed in type I diabetic patients with chronic renal failure. Antilymphocyte globulin or OKT3 was used for induction therapy, followed by standard triple therapy (prednisone, azathioprine, and cyclosporine). Patient and graft survivals were retrospectively analyzed. In addition, a detailed comparison of morbidity in those patients treated after 7/1/87 was performed (53 SPK, 49 KTA). For those less than 45 years of age (65 SPK, 42 KTA), there were no significant differences (P greater than 0.6) in the actuarial patient survival at one year (SPK 92%, KTA 95%), or two years (SPK 89%, KTA 92%), or actuarial renal allograft survival at one year (SPK 82%, KTA 83%) or two years (SPK 77%, KTA 83%). However, for those greater than 45 years old, actuarial renal allograft survival was significantly higher (P less than 0.03) in the KTA group. The mean serum creatinine levels were similar at one year (SPK 1.8, KTA 1.9 mg/d).(ABSTRACT TRUNCATED AT 250 WORDS)