We developed a minimally invasive technique of releasing the piriformis muscle under endoscopic control for entrapment neuropathy of the sciatic nerve because of tension and contraction of the piriformis muscle. This surgical technique was performed in patients who fulfilled at least 5 of 9 diagnostic criteria we established and who did not respond to conservative therapy for 6 months or more. Although a cavity was maintained using a disposable syringe (10 mL) with a cut tip, an arthroscope (4 mm in diameter) was inserted at an oblique viewing angle of 30 degrees, and the muscle was identified. The area from the musculotendinous junction to the muscle was gradually incised using a special scraper. In particular, pain disappeared simultaneously with release of the piriformis muscle during surgery. With this technique, an adequate cavity can be produced and maintained in a manner similar to that in posterior endoscopic surgery for intervertebral disc herniation. This technique is useful for reducing postoperative pain and allows early return to activity.