Giant adrenal myelolipomas are rare, benign, and hormonally inactive tumors. We present the case of a 53-year-old man with a 19-cm retroperitoneal mass, initially suspected to be a retroperitoneal liposarcoma, angiomyolipoma, or adrenal myelolipoma. After conducting endocrine assessments, which were within normal ranges, we decided to perform surgical excision using a modified Makuuchi incision. The tumor was successfully removed, and the final pathological examination confirmed the diagnosis of adrenal myelolipoma. The patient was discharged with no complications and remained without disease recurrence or distant metastasis as of 1 year postoperatively. In conclusion, giant myelolipomas are rare and cause symptoms owing to their large size. Surgical removal is recommended for large or symptomatic myelolipomas. The modified Makuuchi incision allows efficient and safe tumor removal in open surgery for giant myelolipomas.