Exposure to air pollution has been associated with adverse respiratory and cardiovascular health outcomes in both children and adults. In this study, we used geographic information systems (GISs) to explore possible associations between chromosomal damage in 65 African American children and their mothers from Oakland, California, and both proximity to traffic and regional ozone levels. Study participants were interviewed at the Healthy Child Clinic of Children's Hospital, Oakland, and their blood and buccal cells were collected for assessment of chromosomal damage by the micronucleus (MN) assay. Regional ozone levels, which decreased from April to November with a secondary peak in late summer, were highly correlated with season by month (r = −0.84, P = 0.02) and strongly associated with MN frequency (frequency ratio (FR): 3.37, 95% confidence interval (CI): 1.30-8.72) in both cell types of children and adults. Additionally, MN frequencies were modestly associated with individual measures of traffic density in children (FR = 2.45, 95% CI= 0.86-7.10), but not in adults; this suggests a greater vulnerability to traffic-related air pollution in children. Smoking in the household also increased MN frequency in the lymphocytes of children (FR: 1.13, 95%CI: 1.01-1.24) and adults (FR: 1.06, 95%CI: 0.99-1.13), whereas vitamin use in adults decreased MN frequency in both lymphocytes and buccal cells (FR: 0.17, 95%CI: 0.02-1.31; FR: 0.18, 95%CI: 0.03-1.18, respectively). Our data indicate that GIS-generated measures of traffic density for individual households augment regional ozone monitoring data used to assess effects of air pollution. This approach helped to demonstrate elevated cytogenetic damage in exposed minority children.