A 91-year old woman was referred to our hospital for evaluation of a palpable mass in the left hemiabdomen. A marked anemia was found on admission. Imaging revealed an inhomogeneous mass of the left adrenal gland with a diameter of 19 cm. Due to a lack of perfusion in contrast enhanced ultrasound and the clear delineation to neighbouring organs on CT scan, an adrenal hemorrhage was diagnosed. A further fall of hemoglobin level prompted a resection of the mass. The mass consisted of a fibrous wall surrounding hematomas of different age. A small rest of the otherwise normal adrenal gland was found adjacent to the wall. The patient fully recovered. The patient had no underlying cause for the hemorrhage such as trauma, tumor or any coagulopathy including the intake of anticoagulants. Hence, we describe a rare case of spontaneous unilateral adrenal hemorrhage in an elderly woman that was successfully treated by surgery.