Venous aneurysms are less common than arterial aneurysms in clinical practice, and the occurrence of isolated cases is a topic for publication. Aneurysms of the superior mesenteric vein are rare, and their origin is unknown. Many aneurysms are asymptomatic, and the diagnosis is established from radiologic findings. Others are diagnosed after complications such as gastrointestinal bleeding or thrombosis with associated abdominal pain. Because of the rarity of this disease and consequent absence of standard treatment, therapy must be adapted to fit each case. We present a case report of an aneurysm of the superior mesenteric vein. The diagnosis of this anomaly was made after investigation of abdominal pain. Computed tomography (CT) scans demonstrated the mass. Clinical treatment was administered, and no aneurysm growth was observed after 5 years of follow-up.