BACKGROUND Potential benefits of once-daily, prolonged-release tacrolimus over the immediate-release formulation include improved adherence to immunosuppressives post transplantation. An observational study was performed to characterize real-world practice surrounding conversion from immediate- to prolonged-release tacrolimus in kidney transplant recipients. MATERIAL AND METHODS We performed a prospective, observational study of renal transplant recipients converted from immediate- to prolonged-release tacrolimus capsules. Conversion took place at the baseline visit, within the first 6 months of transplantation (early conversion group) or between 6 and 12 months of transplantation (late conversion group). Data collection was performed at routine follow-up at 6 and 12 months. Endpoints included conversion ratio from immediate- to prolonged-release tacrolimus, reasons for conversion, additional visits due to conversion, safety, and tolerability. RESULTS The analysis population comprised 591 patients. Baseline characteristics were similar between the 2 groups. The mean conversion ratio of the daily dose of tacrolimus was 0.98±0.17 in the early group and 0.99±0.09 in the late group. Time from conversion (mean ±SD) to first measurement of trough tacrolimus blood concentration was 12.1±11.6 and 27.6±26.7 days in the early and late groups, respectively. The highest number of additional visits required was 6 in the early conversion group, in 3 patients (0.7%), and 3 in the late conversion group, in 2 patients (1.6%). Conversion from immediate- to prolonged-release tacrolimus was associated with a very low rate of graft rejection. CONCLUSIONS Favorable clinical outcomes and safety profiles were observed with conversion from immediate- to prolonged-release tacrolimus over 1 year following renal transplantation, with no marked differences between the early and late conversion groups.