The aim of the study was to characterize the smoking habit among pregnant women and evaluate the effectiveness of antismoking intervention based on the results of the test "Why am I smoker?". A randomized trial was conducted between December 1, 2000, and December 31, 2001, in public maternity centers in Lódź, Poland. We included into the study all women below 36 weeks of pregnancy who smoke at least one cigarette per day (intervention group - 149 smokers, control group- 144 smokers). The intervention consisted of five visits of the midwife to the home of the smoking pregnant woman. The intervention was based on the results of the test "Why am I smoker?". The results of the test "Why am I smoker?" give the good characteristics of the smoking habit among pregnant women. The intervention based on the results of this test seems to be an effective tool to help them quit smoking.