The mTOR inhibitor sirolimus improves renal transplant function compared with the nephrotoxic calcineurin inhibitors. We evaluated retrospectively the adverse events in 119 of 134 patients getting sirolimus which seemed to be caused by sirolimus. Patients were converted to sirolimus because of malignancies (n = 47), a creeping creatinine (n = 33), or hypertension (n = 26). One cohort had started sirolimus from the time of transplantation (n = 28). A rise in serum lipids and a decrease in hemoglobin were seen relatively regularly, while arthralgia, peripheral edema, gastrointestinal complaints, skin disorders, electrolyte disturbances, and infections occurred only occasionally. Interestingly, 31% of patients developed doubling or more proteinuria. Among renal biopsies, 9/13 showed a glomerulopathy which in 6 cases was de novo and in 3 cases, a presumed recurrence of the primary kidney disease. Thus, we think that caution is required, particularly in connection with preexisting glomerular disease.