Three children presented with low back pain radiating to the leg and with spasm of the hamstring and paravertebral muscles. Since the pain could not be ascribed to trauma, it was necessary to exclude the presence of infection or tumors. All the signs—localization of the pain, tenderness on one side of the back, X-ray film findings of unilateral or bilateral spondylolysis, and localized positive bone scan—pointed to spondylolysis as the cause of pain. All three children exhibited symptoms resembling those found in the facet syndrome described by Mooney and Robertson.