Diagnosis of acute rejection (AR) is difficult during acute tubular necrosis (ATN), and a delay of rejection treatment could result in negative impacts on the renal transplant outcome. At our center, 68 cadaveric kidneys were transplanted during the past 7 years. The 1-, 3- and 5-year graft survival rates were 95.4%, 93.8% and 81.4%, respectively. After the transplants, 16 patients had immediate graft function (G-I), 51 patients experienced ATN for 12.0 +/- 9.3 days, and one patient had a non-functioning graft due to diffuse arteriolar thrombosis caused by DIC in the donor. During ATN, 41 patients had no rejection episodes (G-II) and 10 patients had ARs (G-III). Nine patients were treated with bolus steroid and one with steroid and OKT-3. Although scintigraphic and sonographic examinations were routinely employed, only the histopathological findings of needle biopsies were helpful for the diagnosis of AR during ATN. When the transplant outcome was compared, the serum creatinene level was highest in G-III and lowest in G-I (1.48 vs 1.06 mg/dl, p < 0.05). The posttransplant ATN period was also longer in G-III compared to G-II (23.9 vs 9.1 days, p < 0.005). The 5-year graft survival rate was 85.2% in G-I, 88.0% in G-II and 59.3% in G-III. We conclude that routine serial renal biopsies should be scheduled when ATN develops after the cadaveric renal transplant, since only the histopathological diagnosis is reliable during ATN.