Backround: The exposure of children to passive smoking has shown significant associations to respiratory morbidity. The youngest children between 0 to 2 years of age are usually more affected while with the child’s increasing age a drop in respiratory illnesses incidence and a decrease of the effects of passive smoking are observed. During the repeated investigations of children involved in the ELSPAC study (European Longitudinal Study of Pregnancy and Childhood) the changes of the exposure to environmental tobacco smoke (at children´s age 6, 18 months and 5 years) and the differences in morbidity in the groups with different exposure were assessed. Methods and Results: The data about health indicators and exposure were similarly obtained from the standardized questionnaire filled by mothers and physicians in the 6th, 18th month and in the 5th year of age of children, and assessed for 4 groups of children with different smoking habits of their mothers. The differences were statistically evaluated in the SPSS statistical program. The children of smoking mothers were more often exposed to environmental tobacco smoke; the children of middle and heavy smokers more than the children of light smokers. In the age of six months the children were slightly more often protected from passive smoking exposure than in the age of 18 months and 5 years: the differences were statistically significant (p<0,01). The attendance in kindergarten represents an important protective factor: the children were exposed less during the week-days than during weekends (p<0,001, resp. p<0,01). The respiration symptomatology and morbidity were significantly increased in the earlier periods of life of those children, whose mothers smoked. In the age of 5 years the smoking household environment influences only the higher incidence of asthmatic symptomatology (wheeze breathing, apnoe) and more frequent allergies to household dust and pollen with symptoms of dyspnoe and wheezing (p<0,05). Conclusion: The ELSPAC study has provided evidence of the significant influence of the mother’s smoking on the child exposure to passive smoking. The consequences of such exposure are manifested especially as increased respiratory and allergic morbidity.

        Key words: passive smoking – children – respiratory morbidity - trends