OBJECTIVE: Here we describe a microsurgical method for decompression and the radiological findings of the extraforaminal entrapment of the L5 spinal nerve. METHODS: The authors reviewed the clinical and neurodiagnostic findings, surgical management, and outcomes in 53 patients with extraforaminal entrapment of L5 who had been successfully decompressed via a microsurgical paramedian tangential approach. A total of 28 women and 25men ranging in age from 54 to 73(mean age 65 years). All patients had uni- or bilateral leg pain due to extraforaminal entrapment of L5 in the lumbosacral spine. The mean follow-up period was 9 months (range 3-15 months). RESULTS: Pain was measured by the Numerical Rating Scale. The function of back was assessed by the Oswestry Disability Index score, and the patient satisfaction was evaluated by the North American Spine Society Outcome Questionnaire. Relief of back pain was obtained for all patients immediately after surgery. The mean Numerical Rating Scale improved from 8.2 before the surgery to 1.7 after the surgery (P<0.0001). The mean ODI score improved from 74.6 before the surgery to 15.3 after the surgery (P<0.0001). Overall, excellent and good result were achieved in 27(51%) and 23(43%) at the last follow-up examination. There was no complications related to the surgery, nor was any spinal instability was detected. The parasagittal T-1 weighted magnetic resonance images showed foraminal stenosis with the circumferential loss of the perineural fat signal at L5-1 level in 23 of 53(43%) patients. Radiological and operating finding showed narrowing of the extraforaminal tunnel that resulted from the annulus bulging in 36 patients(68%), disc protrusion or rupture in 17 patients(30%) and osteophytes of the vertebral body in 39 patients(74%). CONCLUSION: The paramedian tangential approach is a safe, effective procedure that avoids the risk of secondary spinal instability. This study showed that the major causes of the extraforaminal nerve root entrapment in the lumbosacral spine are the bulged annulus, the disc protrusion and osteophytes. The major pathognomonic cause of the extraforaminal L5 nerve entrapment was the bulged annulus fibrosus with the osteophytes.