A 50-year-old male patient with a 15-year history of hypertension was referred to our hospital for evaluation of bilateral adrenal tumors. No Cushingoid features were observed. Computed tomographic scan showed 10-mm masses in each adrenal gland. Preoperative endocrinological examinations revealed autonomous cortisol and aldosterone secretion in this patient. The results of a subsequent adrenal venous catheterization study were consistent with the presence of a left cortisol-producing tumor and a right aldosterone-producing tumor. A left partial adrenalectomy was performed initially, but cortisol and aldosterone over-secretion persisted. Accordingly, the patient underwent a right adrenalectomy. Pathological examination of the resected specimens, including immunohistochemical analysis, demonstrated that both adenomas possibly produced cortisol and aldosterone. This is an extremely rare case of bilateral adrenal tumors, in which the left adrenocortical tumor produced and secreted cortisol or both cortisol and aldosterone and the right one produced and secreted both aldosterone and cortisol, as confirmed by clinical findings and pathological studies using immunohistochemical analysis.