PURPOSE:To evaluate the factors influencing the prognosis in avascular necrosis(AVN) of the femoral head by MR. MATERIALS AND METHODS:Radiographic and MRI findings of twenty-three patients(30 cases, aged 23-67 years) with AVN identified clinically and radiologically were evaluated. The radiography included follow up study for at least 6 months. The mean age of these patients was 43 years and M: F ratio was 20: 3. MR imaging was performed at 1. 5T unit using T1- and T2-weighted coronal and Tl-weighted sagittal and axial spin echo sequences. We categorized the changes of the femoral head on radiographic follow-ups to three grades of mild, moderate and severe. We also analyzed the changes of the signal intensity and sizes of the lesion at sagittal and coronal MR images. On MR imaging we classified the extent of AVN of the fernoral head to 2 grades according to the size of lesion. RESULTS:In the cases of mild changes in fernoral head on radiography, the mean age of the patient was 37 years and the extent of AVN was below 1/2 in eleven out of seventeen cases. In the cases of moderate changes, the mean age was 43 years and the extent was above 1/2 in five out of seven cases. In the cases of severe changes, the mean age was 60 years and the extent was above 1/2 in all 6 cases. With 95% confidence coefficient, comparisons in the age and necrosis extent revealed statistical significance in severe versus moderate changes and in severe versus mild changes. Comparisons in the change of signal intensity on T1 and T2 weighted images showed no statistical relationship between each other. CONCLUSION: We conclude that if patient is younger and has smaller extent of the AVN, bone destruction is slower that these factors may be helpful in predicting the prognosis of AVN. However, the modes of the changes of the signal intensity on T1- and T2- weighted images may not be useful in predicting the prognosis of AVN.