PURPOSE: To evaluate potential correlation between the extent and site of avascular necrosis (AVN), as determined by preoperative magnetic resonance (MR) imaging, and the development of femoral head collapse. MATERIALS AND METHODS: Using clinical, radiographic and MR imaging criteria, twenty hips in 15 patients were selected for core decompression. Preoperative MR results were classified into three categories: group A, less than 15% involvement of the weight-bearing portion of the femoral head; group B, 15%-30% involvement; group C, more than 30% involvement, according to ARCO staging. We also established three groups according to site of involvement of the femoral head, namely medial, middle and lateral. RESULTS: Of 20 cases, three were stage Ia; two, Ib; four, Ic; three, IIa; two, IIb; and 6, IIc. Ten cases of Ia, Ib, IIa or IIb showed no femoral head collapse during follow-up of at least 24 months, while ten cases of Ic or IIc showed femoral head collapse. CONCLUSION: The prognosis of core decompression in patients with early AVN is related to the area of lesion in the femoral head.