Pars defect (spondylolysis) of the lumbar spine can cause chronic low back pain, and it sometimes requires surgical intervention. Direct repair is selected for the surgery if young adult patients do not present significant disc degeneration and lumbar instability. In order to lessen damages of back muscles during surgery, we added the use of a spinal endoscope to the "Buck's screwing procedure" the direct repair. There are four steps in this procedure: 1) identification of the defect, 2) curettage (refresh) of the defect, 3) percutaneous insertion of the annulated screws and 4) cancellous bone grafting. All these steps can be done endoscopically. We treated 3 young adults--a baseball player, a professional cycle-racer and a sculptor--using this endoscopic procedure. There were no complications during or after the operation. Union was obtained in all defects within 3 months, and they returned to their previous activities within 6 months after the surgery.