We describe here a 57-year-old woman with a chronic-contained rupture of an internal iliac arterial aneurysm, and this was eroding the sacral neural foramen. Although an isolated internal iliac arterial aneurysm is known to be rare, the ruptured internal iliac arterial aneurysm was diagnosed based on the characteristic radiolgic findings with performing color Doppler ultrasound, MRI and multi-slice computed tomography. The ruptured aneurysm was successfully treated by coil embolization. Color Doppler US, MRI and multi-slice CT are useful for evaluating a mass of a vascular origin that involves the neural foramen.