PURPOSE: To evaluate the efficacy of CT imaging in differentiating pheochromocytoma from primary adrenalcarcinoma and metastasis. MATERIALS AND METHODS: The authors retrospectively reviewed CT imagings of 24 patients(9 males, 15 females, mean age 49) with 27 surgically or clinically proven adrenal neoplasms larger than 3cm indiameter. These neoplasms included pheochromocytomas(n=11), adrenal carcinomas(n=6), and adrenal metastases(n=10,bilateral : 3). Two radiologists visually inspected CT features with respect to tumor size, shape, intratumoral hypodensity, and calcification, and agreed upon their evalvation. These results were compared with the final histopathologic and clinical diagnosis. RESULTS: Ten of eleven pheochromocytomas(91%) were observed to be round or ovoid; this shape was rarely seen in primary carcinomas(0/6) or metastases(2/10). in contrast, mostcarcinomas(6/6, 100%) were lobulated or irregular in shape, as were most metastases(8/10, 80%). smooth, round orovoid intratumoral hypodensity was noted in all pheochromocytomas. Stellate or linear, irregular intratumoral hypodensity was present in all carcinomas and metastases. However, there were no significant differences in CTdensity of calcification. CONCLUSION: Tumor shape and intratumoral hypodensity are very useful CT findings for differentiating adrenal pheochromocytomas from primary carcinomas and metastases.