BACKGROUND Smoking parents of children with asthma frequently report modifying their smoking behavior to reduce their child's smoke exposure. Research has not analyzed the association between parental efforts and the child's smoke exposure. OBJECTIVE To determine passive smoke exposure and the relationship of self-reported parental modifications in smoking behavior to smoke exposure in children with asthma. METHODS Parents of children seen in an inner-city Asthma and Allergy Outpatient Clinic completed questionnaires to evaluate their smoking behavior and modifications they made to decrease their child's exposure to cigarette smoke. Urine specimens were collected from the children to determine smoke exposure as measured by urinary cotinine/creatinine ratios. RESULTS Children from homes with smokers had higher mean urinary cotinine/ creatine ratios than children from smoke free homes (30 versus 4 ng/mg; P = .0005). Cotinine/creatinine ratios increased with the number of smokers in the home. When the parent was the only smoker in the home, the mean urinary cotinine/creatine ratio of children whose parent smoked outside the house was lower than the mean of children whose parent smoked inside (21 versus 51 ng/mg; P = .038). With only one smoker in the home, there was no difference in mean cotinine/creatinine ratios when the primary caregiver was not the smoker versus when the primary caregiver was not the smoker (27 versus 15 ng/mg; P = .10). CONCLUSIONS Smoking outside the house was associated with lower urinary cotinine/creatinine ratio only when the parent was the only smoker in the home.