Adrenocortical oncocytic tumors are rare. As the Weiss criteria overestimate the malignancy of oncocytic tumor due to histological hallmarks, the Lin-Weiss-Bisceglia system (LWB system) is required for an accurate diagnosis of the malignant potential of an oncocytic tumor. We report two cases diagnosed as an oncocytic tumor with uncertain malignant potential (borderline) and an oncocytic tumor (benign) based on the LWB system, both of which were diagnosed as malignant based on the Weiss criteria. Case 1 : A man in his 20s was referred to our hospital for treatment of a left adrenal tumor. A non-functional pheochromocytoma or adrenal cancer was suspected. He underwent surgical resection of the left adrenal tumor and left kidney. The specimen was positive for 3 of the 9 Weiss criteria, but met one minor criterion in the LWB system. He was diagnosed with an oncocytic tumor with uncertain malignant potential (borderline). Case 2 : A woman in her 40s was referred to our hospital for treatment of a left adrenal tumor. Under the possibility of adrenal cancer, she underwent surgical resection of the left adrenal tumor. The specimen was positive for 3 of the 9 Weiss criteria, but the specimen met no criteria in the LWB system. She was diagnosed with an oncocytic tumor (benign). There has been no recurrence of the oncocytic tumor as of 2 years of follow-up in the two patients.