Study Design Literature review. Objectives A review, analysis, and discussion of the extensive literature on lumbar spinal fusion were done to attempt to place in perspective the indications and success rates fur lumbar spinal fusion with and without instrumentation. Summary of Background Data A wide variety of lumbar spinal conditions have been managed by spina! fusion. Results appear better when the diagnosis is very specific and related to definable instability or deformity in patienta with a stable psychologic state. Methods Search of literature. Results Success rates are higher in isthmic spondylolisthesis, unstable spinal stenosis syndromes (degenerative spondylolisthesis, degenerative scoliosis), and in patients with objective segmental instability. Variable success rates are reported for disc-related low back pain conditions and in patients with failed previous surgery. Instrumentation appears to be beneficial in situations where complex deformities or obvious instability is present. When applied for other diagnoses (e.g., internal disc disruption), results appear no better than with traditional surgical techniques. Conclusions The outcome of lumbar spinal fusion depends on careful assessment of the anatomic cause of pain and of the patient's functional state and expectations.