The most common causes of serious low back pain in children include spondylolysis, Scheuermann disease and musculoligamentous injury. Questions should be asked about the mechanism of onset and exacerbating factors, and the frequency, duration and severity of the pain. The examination should check gait and alignment, flexibility, strength and reflexes, and localize and evaluate the pain. Warning signs of serious problems include constant pain in a child younger than 11 years of age that lasts for several weeks or occurs spontaneously at night, repeatedly interferes with school, play or sports, or is associated with marked stiffness and limitation of motion, fever or neurologic abnormalities. Pain at the lumbosacral junction may suggest spondylolysis or spondylolisthesis. Scheuermann disease is diagnosed by the observance of wedging, irregularity or growth disturbance of three successive vertebrae. Musculoligamentous pain may result from injury to or overuse of muscles or joints of the back. Rare causes include discitis, tuberculosis, bone or spinal cord tumor, pyelonephritis and retroperitoneal infection.