Exposure to traffic-related air pollution in urban environment is common and has been associated with adverse human health effects. In utero exposures that result in DNA damage may affect health later in life. Early effects of maternal and in utero exposures to traffic-related air pollution were assessed through the use of validated biomarkers in blood cells from mother-newborn pairs. A cross-sectional biomonitoring study with healthy pregnant women living in the Greater Copenhagen area, Denmark, was conducted. Bulky DNA adducts and micronuclei (MN) were measured in blood from 75 women and 69 umbilical cords, concurrently collected at the time of planned Caesarean section. Modeled residential traffic density, a proxy measure of traffic-related air pollution exposures, was validated by indoor levels of nitrogen dioxide and polycyclic aromatic hydrocarbons in 42 non-smoking homes. DNA adduct levels were similar and positively correlated in maternal and cord blood (1.40 vs. 1.37 n/10(8) nucleotides; r=0.99; p<0.01). Maternal MN frequencies were significantly associated with age (p<0.01), and higher than those of the newborns (7.0 vs. 3.2 MN per 1000 binucleated cells). Adduct levels were highest among mother-newborn pairs who lived near medium-traffic-density (>400-2500 vehicle km/24h; p<0.01) places. MN frequencies among newborns from women who lived at high-traffic-density homes (>2500 vehicle km/24h) were significantly increased (p=0.02). This trend remained after adjusting for potential confounders and effect modifiers. For the first time increased bulky DNA adducts and MN in cord blood after maternal exposures to traffic-related air pollution are found, demonstrating that these transplacental environmental exposures induce DNA damage in newborns. Given that increased DNA damage early in life indicate an increased risk for adverse health effects later in life, these findings justify intervention of pregnant women.