Rectus sheath hematoma is a rare cause of acute abdomen, and its clinical diagnosis is challenging without any imaging methods. We describe a case of a 50-year-old woman with no significant medical history who developed a sudden abdominal pain following a cough paroxysm. On physical examination, there was intense pain after light percussion and tenderness on palpation. Laboratory findings were within normal range. The imaging findings allowed us to diagnose a spontaneous rectus sheath hematoma. A conservative approach was opted. The patient had a favorable course. Accurate diagnosis is of the utmost importance as it may avoid unnecessary interventions, and in some cases, especially for elderly people, it can be fatal. This case alerts us to a rare cause of acute abdomen.