We aimed to investigate the level of knowledge about the effects of cigarette smoking and status before and during pregnancy. The study was performed on 1,020 pregnant women who attended the clinic for a routine visit. The questionnaire consisting of questions about sociodemographic data, smoking habits and knowledge about harmful effects of smoking on fetus (miscarriage, intrauterine growth retardation, pre-term birth, fetal mortality-morbidity, postpartum infant death, pre-term premature rupture of membranes, lung disease, attention deficit) was administered. Data were analysed by SPSS 10.0 using chi(2)-test and binary regression analysis. Mean age was 26.3 years. Smoking rates before and after pregnancy were 34.7% and 14%, respectively. Passive smoking was seen in 69.2%. The number of cigarettes smoked before pregnancy had a significant impact on continuation of smoking during pregnancy [OR (95% CI) 29.94 (12.88-69.64)]. For passive smoking at home for a young age [OR (95% CI) 1.33 (1.01-1.76)] had a positive impact and university education [OR (95% CI) 0.40 (0.24-0.67)] had a negative impact. Most pregnant women (97.5%) knew smoking was harmful. Awareness of intrauterine fetal death as a harmful effect was the single most important factor associated with quitting active and passive smoking. Despite some level of knowledge of pregnant women regarding adverse effects of smoking, there is a strong need for education on quitting smoking during pregnancy. Prevention of passive smoking should have the highest priority.