Micronucleus (MN) frequency is a biomarker for early genetic effects which is often used in humanbiomonitoring studies. Increased frequency of micronuclei has been associated with high levelsof traffic exposure. Further high MN frequency was found predictive for cancer development inseveral studies of adults. In the present study, the MN frequency in blood samples from the Danishparticipants of the European pilot project DEMOCOPHES was analysed and related to the area ofresidence, self-reported and calculated exposure to road traffic as well as to mercury in hair andblood concentrations of persistent organic pollutants and dioxin-like activity measured in the sameparticipants. The MN frequency analysis was performed with the cytokinesis-block micronucleus(CBMN) assay and included 100 children and 119 mothers. We found a significant correlationbetween mothers and children in the levels of micronuclei in 1000 binucleated T lymphocytes(‰MNBN) and in the proliferation index. Further the levels of ‰MNBN were significantly higherin mothers compared with their children. No significant associations were found for ‰MNBNfor traffic related exposure in neither children nor their mothers. In children, a 2.5 times highermicronuclei in mononuclear T lymphocytes were found in children living within 50 m of a busyroad, however, this was not found in mothers or in MNBN and the effect of exposure to road trafficon MN frequency needs further investigation. No significant associations were found between MNfrequencies and the other biomarkers measured in the same participants.