A 48-year-old female with a complain of a palpable left upper abdominal mass was admitted to our hospital. An ultrasonogram revealed a cystic tumor of the liver with septations (10 cm in diameter) in the left lobe. A month after the first examination, another ultrasonogram was performed and a remarkable decrease in the size of the cyst was observed. Aspiration histology was performed with real-time ultrasonic guidance. This procedure revealed a clot within the cyst. Nine months after the first examination, the cyst showed remarkable reduction.