[en] Main objectives of the BfS Project StSch4240 Thyroid Exposure of Belarusian and Ukrainian Children due to the Chernobyl Accident and Resulting Thyroid Cancer Risk were: to establish improved estimates of average thyroid dose for both genders and for each birth-year cohort of the period 1968 - 1985 in Ukrainian and Belarusian settlements, in which more than 10 measurements of the ¹³¹I activity in the human thyroid have been performed in May/June 1986, to explore, whether this dosimetric database can be extended to neighboring settlements, to establish improved estimates of average thyroid dose for both genders and for each birth-year cohort of the period 1968 - 1985 in Ukrainian and Belarusian oblasts (regions) and larger cities, to document the thyroid cancer incidence for the period 1986 - 2001 in Ukraine and Belarus and describe morphological characteristics of the cancer cases, to assess the contribution of the baseline incidence to the total thyroid cancer incidence in the two countries and identify regional and temporal dependencies, to perform analyses of excess risks in settlements with more than 10 measurements of the ¹³¹I activity in the human thyroid. The project has been conducted in the period 6 December 1999 to 31 March 2004. (orig.)