A 27-year-old woman underwent a first vaginal delivery at our institution. She returned four days after delivery, presenting with abdominal pain and an unexplained drop in her hemoglobin value, without external bleeding. The initial computed tomography abdominal scan revealed an isolated diffuse hemoperitoneum. A laparoscopy did not find the cause of bleeding. A second computed tomography scan, performed 15 days later, revealed hemoperitoneum associated with a false aneurysm of the right uterine artery. Treatment consisted of embolization of the uterine arteries, with clinical success. False aneurysms are a rare cause of intra-abdominal non-exteriorized bleeding in late post-partum hemorrhage.