To evaluate diganostic value of triple head (3H) high resolution single photon emission computed tomography(SPECT) for the detection of femoral head avascular necrosis (AVN), Tc-99m MDP planar bone scan, 3H-SPECT and MRI were performed on patients with clinical suspicion of AVN from Mar. 1991 to Jul. 1992 at the Orthopedic Department of Asan Medical Center. 3H-SPECT was undertaken 5 hours after injection of 20 mCi Tc-99m MDP for 20 minutes using three detector rotating gamma camera (TRIAD, Trionix) equipped with ultra-high resolution collimators. Planar bone scan and 3H-SPECT were diagnosed as positive for AVN when a photopenic defect in the femoral head could be identified. Final diagnosis of AVN was established in 32 patients with 52 hips by MRI and pathologic findings. Unilateal disease was present in 11 patients, while 21 had bilateral disease. Of 32 patients and 52 hips, planar bone scan, 3H-SPECT and MRI detected 37, 46 and 52 positive hips respectively. The sensitivity of 3H-SPECT was higher than that of planar bone scan (88.596 vs. 71.5%), and was even comparable to that of MRI (88.596 vs. 100%), and was also higher than previously reported sensitivity of single head SPECT. For hips positive for, AVN, 3H-SPECT image provided greater contrast and defined the lesion site more precisely. Since 3H-SPECT is less expensive than MRI, initial screening for AVN with this technique is preferable, with MRI study resereved for evaluation of extent of disease when 3H-SPECT is positive or, for those cases when strong clinical evidence for the disease exists despite negative screening with 3H-SPECT image. Studies including patients with diseases other than AVN and correlation with other imaging modalities are needed to define more precisely the role of 3H-SPECT in the diagnosis of AVN.