PURPOSE: To determine the incidence of avascular necrosis (AVN) of the femoral head after renal transplantation, evaluate plain radiographic and MR findings, and compare known predisposing factors between the AVN group and the control group. MATERIALS AND METHODS: Between August 1990 and June 1998, 256 renal transplantations were carried out at the Maryknoll hospital. The incidence of AVN was determined clinically, and in the AVN group, plain radiographic and MR findings were evaluated. A control group of 29 cases was randomly selected from among the remaining 241 patients, and acute rejection, mean daily steroid dose and osteopenia were compared between the AVN group and the control group. RESULTS: The incidence of AVN of the femoral head was 5.9 %(15/256). Involvement was bilateral in nine cases and unilateral in six and 24 femoral heads were thus affected. The mean period required for diagnosis of this condition was 10.7 months(within 6 months: 2 hips, between 6 -12 months: 10, between 12 -24 months: 9, over 24 months: 3). Plain radiographs showed that three cases were Ficat stage I, five were stage II, seven were stage III, and nine were stage IV. MRI indicated that 15 cases were Mitchell class A, one was class C, and three were class D. Correlation between Ficat stage and the period required for diagnosis showed that the longer the latter, the higher the Ficat stage. A comparison of risk factors between the AVN group and the control group showed that the incidence of acute rejection and osteopenia, and the mean daily steroid dose, were higher in the AVN group than in the rejection group and that the difference was statistically significant. CONCLUSION: The incidence of AVN of the femoral head after renal transplantation was 5.9 %. The longer the period required for diagnosis of AVN, the higher the Ficat stage. A comparison of risk factors between the AVN group and the rejection group showed that the incidence of acute rejection and osteopenia as well as the mean daily steroid dose, were higher in the AVN group than in the rejection group, and these may thus be pre-disposing factors for AVN. In patients with these risk factors, even though plain radiographic findings are normal, MRI is necessary if AVN is to be diagnosed during its early stages.