Recognizing that not all patients with low back pain have lumbar disc disease, the authors began to inject facet joints in June 1982 and have experience now with 21 patients, each injected under fluoroscopic control with a mixture of local anesthetic and steroid. One technical problem occurred when large osteophytes blocked access to the facet joints. Otherwise, there were no complications and minimal morbidity. Most patients (15 of 20; 75%) had an initial response, but a much smaller number (six of 18 followed more than three months; 33%) had a lasting response. Repeat injections, when done, always led to temporary improvement but rarely to lasting relief (one of five; 20%). Three factors characterized the patients: a negative screening examination for other causes of back pain or sciatica; back pain with tenderness localized over one or more facet joints; and radiologic changes of degenerative joint disease within the facet joints. Facet joint disease may be a significant cause of low back pain. The above three criteria are useful in clinical identification of patients with this problem. Facet joint injections play an important role in the diagnosis and treatment of low back pain.