Cavernous hemangioma of the adrenal gland is a rare tumor, which does not usually have endocrinological function. We report to our knowledge, the third documented case of a functioning adrenal hemangioma. Interestingly, this tumor indicated glucocorticoid hypersecretion, whereas the two previous cases showed mineralocorticoid hypersecretion. The tumor was 5 cm in diameter with typical computed tomography and magnetic resonance imaging findings. Subclinical Cushing's syndrome was diagnosed preoperatively, as there was insufficient suppression of cortisol by low-dose dexamethasone, a low adrenocorticotropic hormone (ACTH) concentration, and diminished ACTH and cortisol circadian rhythms without the typical clinical manifestation and symptoms of hypercortisolism. Intraoperative hypotension occurred immediately after tumor removal and following postoperative adrenal insufficiency, which support that the tumor was hyperfunctioning. The postoperative adrenal insufficiency had recovered completely by 12 months after the operation.