Environmental tobacco smoke ( ETS) contains carcinogenic and toxic agents. Smoking might have a more serious effect on children than adults. We aimed to examine the effects of passive smoking on pulmonary function and respiratory health in children and to assess the concordance between parental self-reported smoking habits and urinary cotinine levels in their children. This cross-sectional study was conducted in the winter with the participation of 131 children (9-12 yr old). The procedure for each subject consisted of administration of a questionnaire to the parents, and collection of a urine sample and measurement of lung function in each child. Cotinine level excreted into urine was analyzed with respect to parental self-reported smoking behavior. Working mothers and mothers with higher level of education tended to smoke more at home (p values, respectively, .002 and .005). There was a statistical difference between the urinary cotinine levels of children when divided into two groups according to their fathers' smoking behavior at home (p = .0001). No statistically significant difference was determined in the mean episodes of respiratory infections treated during the last 12 mo among the groups formed according to daily number of cigarettes smoked by the parents at home (1: not exposed; 2: < 5 cigarettes; 3: 5-10 cigarettes; 4: > 10 cigarettes), or among the groups formed according to urinary cotinine levels (1: < 10 ng/ml; 2: >= 10 ng/ml). No significant difference was demonstrated in any of the respiratory function parameters investigated between the groups considered. The reliability of the declarations of the parents in the estimation of ETS exposure of children was low. Children are unable to remove themselves from ETS exposure. It is better to reduce the percentage of parents who smoke rather than to isolate smokers or increase ventilation.