The aim of the study was to analyze the active smoking by pregnant women in different weeks of pregnancy. The study population consisted of 136 women before 22 weeks of pregnancy. The women were interviewed three times during pregnancy. From all women included into the study the saliva sample was collected three times to verified smoking status in pregnancy. Cotinine level in saliva was analyzes using Liquid Chromatography with Tandem Mass Spectrometry. Based on interview about 25-30% of pregnant women smoked cigarettes during pregnancy. This percentage was higher when the smoking status was verified using cotinine level in saliva (33-41%). In the group of pregnant women who smoked cigarettes there was no decreasing trend in cotinine level during pregnancy whereas in nonsmokers the decreasing trend was observed. Unmarried women, those with lover educational level, and unemployed had the highest risk of smoking during pregnancy.