The rates of childhood thyroid cancer incidence observed in Belarus during the period 1986 to 1995 are described as a function of time after exposure, age at exposure, and sex. Conclusions are drawn for the excess absolute risk function. After a minimum latent period of about 3 years after exposure, this risk function has a linear increase with time for at least 6 years. After correction for the dependence of average doses on age, the radiation-induced absolute thyroid risk in Gomel is about a factor of 3 higher for children up to age 10 at exposure compared to older ones; this may be due in part to different case-collection quality. In addition, in the group up to 10 years at exposure, the thyroid of girls is more sensitive to radiation by a factor of about 1.5 than the thyroid of boys on an absolute scale. Risk estimates from external exposure are consistent with risk estimates from Gomel assuming that the increase in excess cases reaches a plateau soon.