Although neuroendocrine differentiation is a characteristic feature of tumors of the adrenal medulla, cortical tumors may also rarely be differentiated into medullary element. Recently we experienced such a case of adrenal cortical tumor having features of both cortical and medullary tumor. The patient was an 11-year-old girl who was incidentally found to have a left adrenal mass. Laboratory results showed elevated serum cortisol, aldosterone, renin, and epinephrine with high excretion of urinary metanephrine. Urine vanillyl mandelic acid and 17-ketosteroid remained within normal limits. Histologic featuresof a 6 cm round yellowish tumor were ambiguous to decide the orgin of this neoplasm. Cortical element predominated in the tumor with minor areas of pheochromocytomatous feature. Immunohistochemically, the tumor cells were positive for vimentin, neuron specific enolase, and epithelial membrane antigen. Ultrastructural examination revealed scattered membrane bound dense core granules in the tumor cells of medullary differentiation, measuring 150~500 nm in average diameter. Cortical tumor element showed corresponding ultrastructural features. These results indicate that this is a case of adrenal cortical tumor with features of neuroendocrine differentiation.