Ninety-seven children who were diagnosed with acute lymphoblastic leukemia before 10 years of age and treated with chemotherapy alone, chemotherapy plus 1800-cGy cranial irradiation (RT), or chemotherapy plus 2400-cGy RT were evaluated for effects of therapy on dentofacial development. All patients were seen at least 5 years postdiagnosis. Dental abnormalities were determined from panoramic radiographs, and craniofacial evaluations were made from lateral cephalometric radiographs. Ninety-one (94%) of all patients and 41 (100%) of patients younger than 5 years of age at diagnosis had abnormal dental development. The severity of these abnormalities was greater in children who received treatment before 5 years of age and in those who received RT. Observed dental abnormalities included tooth agenesis, arrested root development, microdontia, and enamel dysplasias. Craniofacial abnormalities occurred in 18 of 20 (90%) of those patients who received chemotherapy plus 2400-cGy RT before 5 years of age. Mean cephalometric values of this group showed significant deficient mandibular development. The results of this study suggest that the severity of dentofacial-developmental abnormalities secondary to antileukemia therapy are related to the age of the patient at the initiation of treatment and the use of cranial RT.