OBJECTIVE Heart transplantation remains the gold standard treatment for selected patients with end-stage heart failure. However, transplantation in diabetic patients remains controversial. The hyperglycemic effect of immunosuppressant therapy further complicates posttransplantation management of diabetes and, although this is still unproven, could be responsible for a higher incidence of post-transplantation infection, rejection and mortality. In this study, we aimed to compare one-year outcomes of survival and morbidity after cardiac transplantation among recipients with and without diabetes mellitus. METHODS This was a prospective observational study of 114 patients who underwent first heart transplantation between November 2003 and January 2008, with 1-year follow-up. They were divided into two groups according to whether they had pre-transplantation diabetes (group 1) or not (group 2). Baseline variables and complications were recorded. Logistic regression analysis was used to identify independent predictors of 1-year mortality. RESULTS Of the 114 patients, 33% were diabetic before transplantation. Diabetic patients were older (57.0 +/- 7.4 vs. 51.2 +/- 12.9 years, p = 0.013), and had a higher prevalence of hypertension (63.6% vs. 16.7%, p = 0.002), lower creatinine clearance (53.5 +/- 16.2 vs. 63.0 +/- 21.8 ml/min, p = 0.020) and higher C-reactive protein levels (1.8 +/- 2.4 vs. 0.9 +/- 1.3 mg/l, p = 0.029) than non-diabetics. They tended to have more peripheral arterial disease (20.8 vs. 14.8%, p = NS) and carotid disease (25.8 vs. 14.3%, p = NS). In diabetic patients fasting glucose levels were significantly lower at one year than before heart transplantation (134.2 +/- 45.3 vs. 158.4 +/- 71.2 mg/dl, p = 0.039). There were no significant differences between diabetic and non-diabetic patients in rejection (16.2 vs. 23.4%, p = 0.467), infection (27.0 vs. 33.8%, p = 0.524) or mortality (16.2 vs. 6.5%, p = 0.171) at 1-year follow-up. On logistic regression analysis, the only predictor of 1-year mortality was baseline creatinine > 1.4 mg/dl (OR: 6.36, 95% CI: 1.12-36.04). Diabetes and impaired fasting glucose before heart transplantation were not independent predictors of 1-year mortality. CONCLUSIONS These data suggest that diabetes is not associated with worse 1-year survival or higher morbidity in heart transplant patients, as long as good blood glucose control is maintained.