Almost all working adults, more than half in any given year, experience low back pain. Although the differential diagnosis is extensive, most symptoms have biomechanical causes and resolve promptly with little intervention, although recurrence is common. History and physical examination are important in distinguishing potential causes and identifying "red flags" for more serious conditions. Diagnostic imaging should be ordered only when necessary because of the high incidence of radiologic abnormalities in asymptomatic persons. Once serious illness is ruled unlikely, first-line drug therapy with acetaminophen, a cyclo-oxygenase-2 inhibitor or a nonsteroidal anti-inflammatory drug is recommended. Short-term use of muscle relaxants may be considered, but they can be sedating. Patients should stay as active as possible. Comorbid conditions such as sleep disorders, anxiety, or depression should be treated, and psychosocial issues should be addressed. Opioids should be prescribed if other treatments have been insufficiently effective and if there is evidence of improved function with opioid treatment that outweighs adverse effects. Adjuvant antidepressants and anticonvulsants should be considered, especially in chronic or neuropathic pain. If a structural defect is identified and a diagnostic or therapeutic procedure is available, consider referral. If symptoms have not improved within 4 to 6 weeks, re-evaluation and additional diagnostic workup should be considered.