BACKGROUND Spontaneous rectus sheath hematoma (RSH) is an uncommon and frequently misdiagnosed cause of acute abdominal pain. The purpose of this study is to present our experiences in the diagnosis and treatment of spontaneous RSH. METHODS This is a retrospective study of the medical histories of 15 patients admitted to our emergency surgery unit between January 2000 and July 2009 and diagnosed with spontaneous RSH (12 females, 3 males; mean age, 64.5 years; range, 20-79 years). RESULTS All cases presented with acute abdominal pain or abdominal wall mass, or both. Eleven of the cases (73%) had been receiving some form of anticoagulation therapy. The leading indications for anticoagulation and/or anti-platelet therapy were atrial fibrillation in 5 patients (33%) and mitral valve replacement in 3 patients (20%). Diagnosis was made by abdominal ultrasonography and/or computerized tomography in 14 patients (93%). Twelve (80%) of the 15 patients were discharged uneventfully after conservative management following a mean hospital stay of 8.8 days (range, 3-24 days). The mortality rate was 20%. CONCLUSION Spontaneous RSH must be suspected in patients with advanced age who are using anticoagulation medications and present with acute abdominal pain. Early diagnosis permits conservative management and avoids unnecessary surgical interventions.