Determination of the urinary steroid profile has been proposed as a sensitive tool for diagnosing adrenocortical tumors. The urinary steroid profiles were determined for patients with adrenocortical tumors. Urinary steroids were extracted, derivatized to form methyloxime-trimethylsilyl ether and analyzed by gas chromatography/mass spectrometry. Patients with adrenal adenomas from primary hyperaldosteronism had increased metabolites of 18-hydroxycorticosterone and aldosterone, and those with Cushing's syndrome had elevated excretion of 11 -deoxycortisol, cortisol, 18-hydroxycortisol, and cortisone metabolites. In patients with adrenocortical carcinomas, increased levels of metabolites of 11-deoxycortisol or 33-hydroxy-5-ene steroids were observed. The urinary steroid profiles of adrenal adenomas and adrenocortical carcinomas were quite different, suggesting the diagnostic validity for discriminating malignant from benign diseases.