Pheochromocytoma is a catecholamine-producing tumor which may arise at the same locations in the body where chromaffin tissue has been found to occur. This potentially lethal neoplasm originates in approximately 60% in the adrenal medulla and less frequently 10% are malignant. Pheochromocytoma continues to evoke interest because clinically it is capable of mimiking a variety of syndromes or remaining silent. The clinical manifestations are those which result from the release of catecholamines secreted by the tumor. Epinephrine and norepinephrine are both usually present in adrenal medullary tumors and norepinephrine alone more commonly is secreted by extra-adrenal tumors. Since norepinephrine is a relatively pure alpha adrenergic stimulator and epinephrine has both strong alpha and strong beta adrenergic stimulant effects, clinical manifestations range from hypertension alone to various combinations of tachyarrythmias and hypermetabolism syndromes associated with hypertension. The diagnosis of pheochromocytoma can be confirmed by demonstrating increases in catecholamine or their metabolites. The three most common determinations used for diagnosis are urinary VMA, metanephrine and catecholamines. Radiologic tests included roentgenograms of chest and abdomens, intravenous pyelography, nephrotomogram, arteriography and CT are helpful in diagnosis. Recently scintigrams using a new radiopharmaceutical agent, [131I] metaiodobenzylguanidine([131I] MIBG) is appealing because they not only locate the anatomic position of the disease but also shed light on the nature of the disturbance by providing evidence of function, this procedures are safe. The treatment of pheochromocytoma is only surgical excision. The surgical mortality is approximately 2.9% and 5 years survival subsequent to treatment of the benign tumors was 96%. The purpose of this paper is to report two cases of pheochromocytoma with characteristic clinical manifestations and teated at Presbyterian Medical Center, Taegu during last tow years and review briefly the literatures.