With the widespread use of non-invasive imaging modalities, the incidental detection of myelolipoma has become more common. We analyze the clinical data of 4 typical cases of unilateral adrenal myelolipomas, including 1 hormonally inactive patient and 3 hormonally active cases with hyperaldosteronemia, hypercortisolism and hyperandrogenemia. Obvious differences were found in the pathological sections. To our knowledge, this is the first article discussing the etiology of adrenal myelolipoma from pathologic analyses.