A retrospective review was performed of radionuclide bone scans and radiographs of 54 children with diagnoses of spondylolysis or osteoid osteoma/osteoblastoma. The findings indicate that skeletal scintigraphy shows imaging patterns that can be used to help distinguish these two conditions. Most cases of spondylolysis and all cases of osteoid osteoma or osteoblastoma demonstrated focally increased activity on the delayed skeletal scintigrams. Evaluation of the bone scan images obtained during the immediate postinjection period revealed intense activity with osteoid osteoma and osteoblastoma, but minimal or no abnormal activity in cases of spondylolysis. In addition, spondylolysis was the only condition that produced bilateral abnormalities in the pars interarticularis region in these children.