The dental status of 16 children who had been treated with bone marrow transplantation (BMT) for serious bone marrow diseases was followed for up to 6 years. Several types of disturbances in dental development were observed in children who had been conditioned with total body irradiation (TBI) at 10 Gy before BMT. Thus, impaired root development that caused short V-shaped roots was found in all patients, a complete failure of root development and premature apical closure were found in five patients, enamel hypoplasia was observed in four patients, and microdontia was observed in three patients conditioned with TBI. Patients younger than 6 years of age at BMT exhibited the most severe and extensive dental aberrations. The TBI at 10 Gy appeared to be the major cause of the disturbances found.