Low back pain is common, but a herniated intervertebral disk is the cause in only a small percentage of cases. Most symptomatic disk herniations result in clinical manifestations (pain, reflex loss, muscle weakness) that resolve with conservative therapy, and only 5% to 10% of patients require surgery. Sciatica is usually the first clue to disk herniation, but sciatica may be mimicked by other disorders that cause radiating pain. Because more than 95% of lumbar disk herniations occur at the L4-5 or L5-S1 levels, the physical examination should focus on abnormalities of the L5 and S1 nerve roots. Plain radiography is not useful in diagnosing disk herniation, but more sophisticated imaging (myelography, computed tomography, or magnetic resonance imaging) should generally be delayed until a patient is clearly a surgical candidate. Conservative therapy includes nonsteroidal anti-inflammatory drugs, brief bed rest (often for less than 1 week), early progressive ambulation, and reassurance about a favorable prognosis. Muscle relaxants and narcotic analgesics have a limited role, and their use should be strictly time-limited. Conventional traction and corsets are probably ineffective. Except for patients with the cauda equina syndrome, surgery is generally appropriate only when there is a combination of definite disk herniation shown by imaging, a corresponding syndrome of sciatic pain, a corresponding neurologic deficit, and a failure to respond to 6 weeks of conservative therapy.