BACKGROUND: Little is known about the level of tobacco exposure and the factors that influence exposure in children with persistent asthma. OBJECTIVE: We sought to measure tobacco smoke exposure and determine factors associated with exposure in a large urban sample of asthmatic children. METHODS: This cross-sectional study is based on a community-based cohort of 482 children (8-14 years old) with persistent asthma. Caregiver and household tobacco use were reported by the caregiver. Child tobacco smoke exposure was assessed by using salivary cotinine level. Multivariate linear regression of log-transformed salivary cotinine levels were used to characterize the relationship between smoke exposure and caregiver, household, and demographic characteristics. We used a multivariate logistic model to characterize associations with caregiver smoking. RESULTS: Overall, 68.5% of children had tobacco smoke exposure. Compared with nonexposed children, those exposed to smoking by a caregiver or another household member had cotinine levels that were 1.68 (95% CI, 1.45-1.94) or 1.40 (95% CI, 1.22-1.62) times higher, respectively. Compared with Hispanic children, African American and white/other children had 1.55 (95% CI, 1.16-2.06) and 1.59 (95% CI, 1.18-2.14) times higher cotinine levels, respectively. Child exposure was also associated with caregiver depression symptoms (odds ratio, 1.01; 95% CI, 1.01-1.02), and higher household income was protective (odds ratio, 0.73; 95% CI, 0.56-0.95). Independent predictors of caregiver smoking included a protective effect of higher education (odds ratio, 0.35; 95% CI, 0.15-0.83) and a positive association with potential problematic drug/alcohol use (odds ratio, 2.30; 95% CI, 1.39-3.83). CONCLUSIONS: Tobacco smoke exposure was high in this urban sample of asthmatic children. Caregiver smoking was strongly associated with child exposure and also was associated with lower socioeconomic status, non-Hispanic ethnicity, and depression symptoms.