Background: Abdominal apoplexy is a rare clinical entity, and its clinical manifestations are diverse. Case report: A 52-year-old man developed severe right upper abdominal pain with unstable hemodynamics 24h after right upper pulmonary lobectomy for a lung carcinoma. Abdominal ultrasound and computed tomography (CT) were performed before exploratory laparotomy. Abdominal CT showed a ruptured right gastric artery aneurysm, which was confirmed by exploratory laparotomy. Three liters of blood was drained from the abdominal and pelvic cavity, and the offending artery was ligated. The patient had a full recovery. Conclusions: Abdominal apoplexy may present with non-specific symptoms. Abdominal ultrasound and CT scan are the diagnostic tests of choice. Laparotomy should be performed in a timely manner when the diagnosis is suspected.