We report a 66-year-old woman with a mixed corticomedullary tumor of the left adrenal gland. The patient was found to harbor an adrenal incidentaloma while investigated for a spigelian hernia. Due to the atypical radiological features and the relatively large size of the adrenal lesion she underwent a left adrenalectomy following endocrine testing to exclude a functional lesion. Subclinical Cushing's syndrome was suggested by the failure to obtain adequate cortisol suppression (less than 1.8 microg/dL) following dexamethasone administration pre-operatively; cortisol suppression was restored postoperatively following the excision of the tumor. Histology was consistent with a corticomedullary mixed adenoma, a lesion for which, there is paucity of published data regarding its natural history and long term outcome. The finding of this case highlights the importance of this extremely rare entity which should be included in the long list of causes of adrenal incidentaloma since cases with intra-operative complications have been described. The previously reported reappearance of this tumor in the contralateral adrenal gland emphasizes the need for prolonged follow-up.