Adrenocortical oncocytoma is found very rarely. Most such tumours are benign and nonfunctioning. We report the case of a nonfunctioning adrenocortical oncocytoma located in the right adrenal gland in a 35-year-old man. The patient was tested because of arrhythmia. An adrenal mass of 68 × 64 mm was found during ultrasonography, followed by CT examination. Physical examination indicated obesity with BMI of 32.8 kg/m(2). Abnormal laboratory findings based on an oral glucose tolerance test revealed impaired glucose tolerance and elevated cholesterol level. The patient underwent a laparotomy for a pathological mass located in the right adrenal gland. The pathology report confirmed adrenocortical oncocytoma of uncertain malignant potential. The patient is still alive with no metastases, 37 months after the surgery. Adrenocortical oncocytoma, although extremely rare, should be considered in the differential diagnosis of adrenal tumours.