An attempt was made to recognize entrapment of the lumbar root within the root canal using four criteria; (1) severe, constant root pain to the lower leg, (2) pain unrelieved by bed rest, (3) minimal tension signs, and (4) patients over 40 years of age. Two hundred forty-nine patients fulfilled the criteria, representing 11% of patients attending a back pain clinic. Most had restricted spinal extension, but few had abnormal neurologic signs. Degenerative change was common, especially disc space reduction. Central canal size measured by ultrasound was normal, compatible with a variable past history of back pain. Patients with a long history of back pain numbered 80%, and 90.4% were managed by nonoperative means. Although 78% of these still had some root pain between 1 and 4 years after first attendance, most of them were not troubled sufficiently to have sought alternative help.