Myelolipomas of the adrenal gland are benign, nonfunctioning tumors. Patients with congenital adrenal hyperplasia sometimes develop large and bilateral myelolipomas. Although the precise pathogenesis of myelolipomas remains unclear, prolonged stimulation with high levels of adrenocorticotropic hormone (ACTH) or adrenal androgens are assumed to have a causative role. To clarify the role of ACTH and androgen in the pathogenesis of myelolipoma, we report a case of giant adrenal myelolipoma in a patient with poorly controlled congenital adrenal hyperplasia. A 43-year-old female was diagnosed with congenital adrenal hyperplasia at 6 years of age because of ambiguous genitalia. She had high plasma ACTH and 17-hydroxyprogesterone levels. Abdominal computed tomography showed a huge mass on the left adrenal gland, and an enlarged right adrenal mass. Genetic testing for CYP21A2 was performed and revealed that her genotype was IVS2–13A/C>G/I172N. Adrenalectomy for the left-side tumor was performed. Histological study revealed that the tumor consisted of fat cells and myeloid components, findings compatible with adrenal myelolipoma. Neither ACTH receptors nor androgen receptor was over-expressed in the tumor. Our finding that the tumor did not over-express ACTH or androgen receptor suggests a limited direct role for these hormones in the development of the myelolipoma.