Fifty-two long-term survivors of childhood leukemia or solid tumors had a clinical dental examination along with 49 of their sibling. The 52, with an additional 30 examined in a previous study, were studied radiologically with a panoramic tomogram. All children with leukemia had received chemotherapy for 2 or 3 years and irradiation on standard protocols and the solid tumor group had received chemotherapy for 6 to 24 months. There was no difference between siblings and patients for dental caries, gingivitis, and oral hygiene, mouth opening, overjet, and overbite. More solid-tumor patients had abnormal occlusion (P less than 0.02) and those with abnormalities tended to have been treated at an earlier age. Enamel opacities and hypoplasia were more common in patients than siblings and in the leukemia than in the solid tumor group. Sixty-five percent of the children had abnormalities on radiologic examination including failure of the tooth to develop, small crown, hypoplasia of the crown, and abnormal root development. In most cases the radiologic abnormality could be correlated in time with the patient's treatment and a knowledge of the normal time of tooth development. Three teeth extracted during the course of the study were examined histologically and these showed prominent incremental lines which could be correlated in time with vincristine treatment.