Rectus sheath hematoma is an unusual but well-known clinical problem. Our hospital admitted a 54-year-old woman complaining of harsh right-sided hypogastric pain that started while muscle training. Computed tomography of the abdomen and pelvis demonstrated a right rectus sheath hematoma. As the hematoma did not increase, the patient was conservatively treated. Despite increased awareness of rectus sheath hematoma, its early diagnosis and treatment still present a challenge to emergency physicians. Swift acknowledgement of this rare cause of abdominal pain may avoid more intrusive examination, unnecessary hospitalization, and laparotomy. Careful consideration of the patient's medical history and a high index of suspicion are needed to diagnose this complication.