Abstract Adrenal cysts are a rare condition and are usually non-functioning and asymptomatic. A 44-year-old man was referred from another hospital because a left retroperitoneal tumor was incidentally found by abdominal echography. Laboratory findings including adrenal hormonal study were within the normal range. It showed homogeneously low intensity on T1-weighted images and high intensity on T2-weighted images on magnetic resonance imaging (MRI). Angiography demonstrated that the tumor was avascular and of left adrenal origin. The patient was diagnosed with left adrenal cyst and was intensively followed up with plans for examination with diagnostic imaging.