An 85-year-old woman was admitted to the hospital with a diagnosis of cardiac failure. Abdominal distention and vomiting developed during hospitalization, and the patient was transferred to the surgical ward after a diagnosis of ileus was made. X-ray film of the abdomen showed the presence of ileus; the How-ship-Romberg sign was negative, however. Ultrasonography, computed tomography, and magnetic resonance imaging performed preoperatively all led to a diagnosis of an incarcerated obturator hernia. Surgery
was performed to repair a partially incarcerated obturator hernia of the Richter type on the left side. There
were no postoperative complications, and the patient recovered smoothly. Because of its simple adiministrative nature, we concluded that of the three preoperative tests used (ultrasonography, computed tomography, and magnetic resonance imaging) ultrasonography is the most useful in the preoperative diagnosis of obturator hernia.