To determine whether magnetic resonance imaging (MRI) can demonstrate the early stage changes of avascular necrosis of the femoral head that are not detectable radiographically. Clinical examinations, radiography and MRI were performed in twenty-six patients (thirty hips) at high risk. On the basis of the pathological findings of core biopsies, the results demonstrate that MRI had an accuracy of 96.7% in diagnosing pre-radiologic stage necrosis of the femoral head in this series.