Lumbar facet joints are difficult to image with conventional radiographic techniques. A series of 100 consecutive cases of low back pain and sciatica was examined with CT. Abnormal facet joints were found in 65. Abnormalities demonstrated by CT included osteophyte formation, hypertrophy of articular processes, articular cartilage thinning, vacuum joint phenomenon, and calcification of the joint capsule. In patients with sciatic or low back pain, CT is indicated to demonstrate treatable abnormalities of the facet joints.