BACKGROUND: Computed tomography(CT) is currently considered as the initial imaging procedure of choice for the localization of pheochromocytomas in most of the cases. 131I-or 123I-Metaiodobenzylguanidine scintigraphy(MIBG scan) was proven to be a highly specific tool for the detection of adrenal and extra-adrenal pheochromocytomas, but was less sensitive than CT. The present study is aimed to evaluate the usefulness of a MIBG scan in diagnosis and localization of pheochromocytoma when compared to CT. METHODS: We retrospectively evaluated 27 patients who underwent a MIBG scan for a pheochromocytoma at the Seoul National University Hospital from the year 2000 and 2002. According to the pathological and clinical findings, in 16 the patients pheochromocytoma was confirmed to be positive and the rest 11 of the patients were excluded from the study. RESULTS: Pheochromocytomas was identified in 16 patients. Eleven of them were localized in adrenal gland and 5 were extra-adrenal lesions. The sensitivity to MIBG scan in adrenal lesions and extra-adrenal lesions, was 72%(8/11) and 40%(2/5) respectively. In our study, the overall sensitivity to MIBG scan was 62%(10/16), and overall specificity was 90.9%(10/11). By CT four were identified to have equivocal biochemical abnormalities, but were definite and extraadrenal tumors by MIBG scan showed abnormal uptakes in two of them. CONCLUSION: The MIBG scan was especially useful in 2 of the 27 patients but we had no experienced about the additional benefits of a MIBG scan in the other 25 cases. Our results reveal that a MIBG scan should be performed carefully for the diagnosis and localization of a pheochromocytoma, while considering cost and time of operation.