Oncocytic tumors are rare in the adrenal gland. The histopathological diagnosis of adrenocortical carcinoma is difficult due to the lack of precise diagnostic criteria for malignancy. A 44-year-old man was admitted to our hospital with left flank pain. Radiologically an adrenal mass was detected. After the excision and histopathologic evaluation of the mass, a diagnosis of adrenocortical oncocytic carcinoma was made. At least one of the features of more than 5 mitoses in 50 high power fields, atypical mitotic figures or venous invasion is required for the diagnosis of malignancy in adrenocortical tumors. It has been suggested that tumors that have more than one of the minor criteria of large size (>10 cm or >200 gr), necrosis, capsular or sinusoidal invasion, should be evaluated as having uncertain malignant potential.