A number of studies have been conducted on atomic bomb (A-bomb) survivors in Hi-roshima and Nagasaki, evaluating the late influence of ionizing radiation on humans. The enormous atomic bomb explosion caused massive destruction and loss of lives in Hiroshima in 1945. The present study was conducted to examine the relationship between radiation exposure and prevalence of congenital missing teeth. Six hundred seventy-eight orthodontic patients (212 males, 466 females), had registered in our clinic. Questionnaires were used to the enrollers for the examination. Generally, the number of female patients with congenital missing teeth were greater than that of males. In our study, the number of patients with congenital missing teeth was found to be significantly higher in the radiation exposed affected families compared to that of non-affected ones. In these radiation exposed families, male subjects also exhibited higher prevalence of congenital missing teeth than the females of the non-affected families. These findings suggest that the higher rate of missing teeth in the offspring of Hiroshima atomic bomb survivors is possibly the consequence of the exposure of ionic radiation.