The aim of the study was to evaluate the prenatal and postnatal child exposure to environmental tobacco smoke. The study population consisted of 83 women from Lodz, Poland among which detail questionnaire was conducted three times during pregnancy period. From all women included into the study the saliva sample was collected to verify smoking status in pregnancy. One year after delivery the second questionnaire was performed and urine sample from all children was collected. The cotinine level in saliva and urine was analyzed using Liquid Chromatography with Tandem Mass Spectrometry (LC-MS/MS ESI+). About 22% of the children were expose to ETS during prenatal and 46% in postnatal period. Cotinine level in children's urine statistically differentiated children from smoking mothers (Geometric Mean (GM) 11.4 ng/ml; 95% CI 7.1-18.3) and exposed homes (GM 7.3 ng/ml; 95% CI 3.6-15.0) compared with non-exposed homes (GM 1.3 ng/ml; 95% CI 0.9-1.7) (p < 0.001). Children should be more protected from ETS exposure in prenatal and postnatal period.