The operative failures and complications of percutaneous posterolateral lumbar discectomy were analyzed in 100 patients who had a herniated nucleus pulposus and were prospectively studied and treated with use of a 6.9-millimeter outer-diameter (4.9-millimeter inner-diameter) sheath and manual insertion of the instruments. Twelve operations were considered to have failed, regardless of the length of postoperative follow-up or the incidence of reinjury; eleven patients had a repeat operation at the index level, and one patient was a chronic drug-abuser. In eight of the eleven patients, subsequent laminectomy was successful. Two patients had a psoas hematoma and one had a transitory sensory and distal motor deficit; all of these complications resolved without sequelae. There were no major complications, including superficial or deep infection, and no patient had neurovascular compromise.