We studied three cases of adrenocortical neoplasms that were detected incidentally after radiological examination of the abdomen. These cases did not demonstrate any clinical evidence of adrenocortical abnormalities, such as virilization. Macroscopically, the tumors were light to dark tan on cut surface. Light-microscopic examination revealed compact cells with abundant lipid-sparse eosinophilic cytoplasm and occasional enlarged nuclei. In one case, ultrastructural observation demonstrated abundant mitochondria. Immunohistochemical examination of all of the adrenocortical steroidogenic enzymes showed that none of the cases had immunoreactivity. No mitotic activity and no vascular invasion was observed. The postoperative course were uneventful. The follow-up interval varied from 8 to 27 months. These three neoplasms apparently represent the first reported cases of adrenocortical oncocytoma. They can be considered true nonfunctioning adrenocortical neoplasms because steroidogenic enzymes required for corticosteroid biosynthesis were not expressed in the tumor cells.