The case of a 58 years-old woman with incidental adrenal tumor without endocrinological features of Cushing's syndrome, dexamethasone nonsuppressible uptake of 131I-19 iodocholesterol on right adrenal gland, and no uptake of the left, is described. Right adrenalectomy was performed with the diagnosis of adrenal tumor. The histopathological study revealed that the mass was an adrenal adenoma composed of mixtures of clear and compact cells. Postoperative course was uneventful without replacement therapy with cortisol. This case report suggest that in patients with incidental adrenal tumor, the adrenocortical scintigraphy is very useful for the identification for autonomously functioning adrenal mass.