The measurement of micronuclei (MN) in umbilical blood lymphocytes of newborns are increasingly used in cytogenetic epidemiology as one of the preferred methods for assessing chromosomal damage resulted from maternal exposure to mutagen. In the present study, we evaluated the effect of strong environmental contamination (EC) (which occured in the City of Kragujevac, Central Serbia in 1999) on the MN frequency in group of 22 newborns born in Kragujevac 18 years after EC, using cytokinesis-block micronucleus (CBMN) assay. The mean MN frequency in umbilical lymphocytes of these newborns was 5.14 ± 2.17/1,000 binucleated (BN) cells, which is significantly lower than mean MN frequency of newborns born 12 months after contamination (9.36 ± 5.60/1,000 BN cells). Sex of newborns, age of mothers, cigarette smoking, and number of pregnancies did not affect the MN frequency of newborns. Our results showed that in utero exposure to environmental pollution affected genome instability of the fetuses, but that by improving the quality of environmental conditions there was a decrease in mean MN frequency of newborns born 18 years after contamination. In general, genome of umbilical lymphocytes shows a realistic picture of all changes in body and the environment.