The prevalence of post-transplant diabetes mellitus in 222 consecutive live related renal allograft recipients over a 3-year period was found to be 11.7%. Most of them (20 of 26) developed diabetes mellitus within the first 4 months of transplantation. Post-transplant diabetic patients were older, and had a significantly greater incidence of avascular necrosis of bone. An assessment of risk factors showed that abnormal postprandial blood sugar pretransplant was a significant predictor for development of post-transplant diabetes, whereas cumulative oral steroid dose, weight gain after transplant, type of immunosuppression employed, and graft function were not important. We conclude that post-transplant diabetes mellitus frequently develops in patients with a predisposition by virtue of older age and pretransplant postprandial hyperglycaemia. While steroids are important in the pathogenesis, there was no demonstrable dose-response relationship; post-transplant diabetic patients may be a group with a greater propensity to steroid-induced complications.