The purpose of this study was to determine the efficacy and feasibility of posterolateral percutaneous endoscopic lumbar foraminotomy (PELF) for foraminal or lateral exit zone stenosis of the L5-S1 level in the awake patient. Twelve consecutive patients with L5-S1 foraminal stenosis and associated leg pain underwent PELF between May 2001 and July 2002. Under fluoroscopic guidance, posterolateral endoscopic foraminal decompression was performed using a bone reamer, endoscopic forceps, and a laser. Using this new technique, the authors removed part of the hypertrophied superior facet, thickened ligamentum flavum, and protruded disc compressing the exiting (L-5) nerve root. Clinical outcome was measured using the Macnab criteria. The mean follow-up period was 12.9 months. All the patients were discharged within 24 hours. Satisfactory (excellent or good) results were demonstrated in 10 patients. There was no complication. The PELF procedure provides a simple alternative for treating lumbar foraminal or lateral exit zone stenosis in selected cases. The authors found that the posterolateral endoscopic approach to the L5-S1 foramen was usually possible and that using a bone reamer to undercut the superior facet was effective.