A woman in her 30s with a history of chronic hepatitis B was found on computed tomography to have a 13-cm retroperitoneal mass on her left side with a significant mass effect. The patient was symptomatic with intermittent left upper quadrant abdominal pain that was associated with nausea and constipation. She reported no other gastrointestinal, genitourinary, or overall symptoms. In addition to chronic hepatitis B, her medical history was notable for hypertension and her surgical history was significant for a recent liver biopsy. Physical examination revealed a soft, nontender, minimally distended abdomen with no palpable masses and no costovertebral angle tenderness.