In this study we investigated the influence of a tacrolimus (TAC) plus mycophenolate mofetil (MMF) immunosuppressive regimen on the acute rejection rate and side effect profile in renal transplant recipients. The study included 80 living-related and 40 cadaveric donor renal transplant recipients (82 men, 38 women) of mean age 35 +/- 10 years (range, 16 to 58) who were operated between August 1999 and September 2002. The mean HLA mismatches was 3 +/- 1 (range, 0 to 5). All patients received prednisolone, MMF (2 g/d for the first 14 days posttransplant and then 1 g/d) plus TAC (0.2 mg/kg/d). They were followed for the development of rejection attacks and side effects. Diabetes mellitus developed in 13 patients (9 men, 4 women; 10.8%). Initially, patients required insulin therapy but after 6 months, 5 recipients no longer needed insulin therapy and were switched to oral hypoglycermic agents and diet control. Hypertension was diagnosed in 58 patients (48.3%). Neither gender nor donor origin (P =.14; P =.79, respectively) produced a significant difference in diabetes mellitus development. Biopsy proven acute rejection episodes were observed in 16 out of 120 patients (13.3%). Six out of 120 patients lost their grafts throughout the study period including one death because of suicide, one because of cytomegalovirus disease and hemophagocytic syndrome, one due to posttransplant lymphoproliferative disease and two to a cardiac arrhythmia. Only one patient lost his graft due to acute accelerated vascular rejection. Biopsy-proven chronic rejection appeared in one patient. In conclusion, although the incidence of insulin-dependent diabetes mellitus during posttransplant 6 months, seems high it decreased to 1.6% upon reduction of the TAC dosage. TAC plus MMF immunosuppression seems effective and safe in terms of acute rejection rates and side effect profiles.