The Institute for Medical Protection of Mothers and Children, being regional centre of European registry of congenital malformations (EUROCAT) since 1982, registers congenital anomalies in municipals of Varazdin and Rijeka. Following the nuclear disaster of Chernobyl, there were numerous articles published mainly in daily newspapers, pointing to the increased number of malformations, particularly to Down's syndrome, due to additional irradiation imposed on population. Through this study we wanted to find out whether in Varazdin and Rijeka, following the Chernobyl's accident, there has been any increase of congenital anomalies and whether our regional and EUROCAT registry have been adequate to find out genetic effects of small doses of ionizing radiation. The total incidence of registered congenital anomalies in Varazdin and Rijeka in previous four-year period, amounted to 12.97%, while following Chernobyl, it amounted to 12.7%. Not even nine marker malformations, including Down's syndrome, show any statistically significant increased number of malformations, a year after this nuclear accident. In 18 EUROCAT registries, on almost half a million of newly born children and foetuses, conceived before and after May 1, 1986, the frequency of Down's syndrome and congenital malformations of central nervous system and eyes has been compared. There have been no important differences between two compared groups, and the rate of Down's syndrome was 1.26% before, and 0.91% after the accident. Anticipated stochastic genetic effects of measured and estimated additional doses of radiation imposed to our and Western European populations are too small to be found out neither by regional nor by EUROCAT registries.