One of the rarest situations regarding an adrenal incidentaloma is an adrenal cyst. We present the case of a 61Z–year old male patient diagnosed with peritonitis. During surgery, a right adrenal tumor of 2 cm is discovered. The patient was referred to endocrinology. 6 months later the diameter of the tumor is 7 times bigger than the initial stage. It has no secretory phenotype, except for the small increase of serum aldosterone and the 24–h 17–ketosteroids. Open right adrenalectomy is performed and a cyst of 15 cm is removed. The evolution after surgery is good. The pathological exam reveals an adrenal cyst with calcifications and osteoid metaplasia. The immunohistochemistry showed a positive reaction for CD34 and ACT in the vessels and VIM in the stroma. The adrenal cysts are not frequent and represent a challenge regarding the preoperative diagnostic and surgical procedure of resection. The pathological exam highlights the major aspects.