Eighty-one patients under the age of 20 years who underwent fusion for symptomatic spondylolysis and spondylolisthesis were evaluated. Sex distribution was equal. Initial symptoms included back pain in 90% of patients, radicular pain radiating to an L5 or S1 nerve root distribution in 57%, and back deformity in 46%. Physical findings included diffuse lumbosacral tenderness in 70% of patients, increased lumbar lordosis in 63%, and neurologic deficit of an L5 or S1 nerve root in 16%. Roentgenograms demonstrated lytic pars interarticularis defects in 9% of patients without olisthesis, while 35% had slips of greater than one-half the width of the sacrum. Radiographic nonunion after fusion was diagnosed in 15% of patients. Spastic cerebral palsy and increased length of fusion predisposed to nonunion, while severity of olisthesis and ambulatory treatment postoperatively could not be implicated. The final results of fusion were both subjectively and objectively satisfactory. Eighty-one percent of patients had no or very mild pain which did not interfere with activity, while 16% required occasional salicylates and only 2%, stronger analgesics. Ninety-one percent participated in athletics, and 73% of patients were employed at work which involved prolonged standing or sitting. Physical examination 5 years postoperatively in 27 patients demonstrated no evidence of hamstring spasm, supple spines, and only mild incisional tenderness. Neurologic examination was normal in all but 1 patient who remained unchanged following fusion 9 years previously.