For medical reasons, encouraging women to stop smoking during pregnancy and post partum has high priority. Many smokers want to stop smoking but decline clinical treatment when it is offered. The aim of this study was to find a method which was accepted by a large number of smokers, had a high success rate and, at the same time, required little involvement from personnel. For one year, all pregnant smokers attending 13 of the 14 public health maternity clinics in Gothenburg for their first appointment were invited to participate in this study. Inclusion criteria were daily smoking, a gestational age of less than 12 weeks and ability to understand Swedish. A total of 745 women was registered, but 22 of them stopped smoking before the treatment. The remaining women were randomized to a treatment group (n = 492) and a control group (n = 231). Of the 492 women in the treatment group 417 (85%) accepted the idea of using the self-help manual written especially for pregnant women and given to each woman in the treatment group by the obstetrician. Overall 10.4% of the treatment group stopped smoking up to 8 weeks after delivery compared with 5.2% of the control group (odds ratio 0.5, 95% CI 0.2-0.9). The ex-smoking status was verified by measurement of thiocyanate in blood. The self-help manual had a high acceptance rate and a success rate that was double the rate in the control group.