The most common cause of pain in the distribution of sciatic nerve is a herniated lumbar disc, Spinal stenosis, intrapelvic masses, and diabetic neuropathy may also produce scitica-like symptom. Infrequently, Piriformis syndrome is a rare disease causing sciatica produced by entrapment of sciatic nerve by the piriformis muscle as it passes through the sciatic notch. Recently we experienced a case of piriformis syndrome to be successfully treated by exploration of sciatic nerve and sectioning of fibrous band between piriformis muscle and gluteus maximus muscle. We would describe the clinical feature of a piriformis syndrome, and review other literatures.