A 24-year-old woman with non-pituitary dependent Cushing's syndrome was found to have bilateral adrenal myelolipomas at surgery. These benign tumors consist of bone marrow and fat and are uncommon incidental findings that are discovered by computed tomography. Myelolipomas have rarely been associated with Cushing's syndrome, but the cause of the syndrome has not always been defined, because the reports preceded modern diagnostic methods. Careful examination of the adrenal glands from our patient showed a fusion of myelolipoma elements and adrenal cells without distinct adenomas or the typical nodular pattern of adrenal hyperplasia. This report suggests that adrenal myelolipomas and atypical hyperplasia of the zona fasciculata may be anatomically and functionally related.