Objective To assess the effects of smoking during pregnancy on coagulation and fibrinolysis. Design A cross‐sectional study. Setting A teaching hospital in Heerlen, The Netherlands. Results Parameters of coagulation activation increased significantly with gestational age. The values presented are median values. Prothrombin fragment 1+2 increased from 0.8 to 25 nmol/l in the nonsmoking group of pregnant women and from 1.0 to 1.8 nmol/l in the smoking group. Thrombin‐antithrombin III (TAT) levels increased from 2.2 to 9.9 μg/l in the nonsmoking group and from 3.1 to 8.5 μg/1 in the smoking group. Parameters of fibrinolysis showed a different picture. Plasminogen levels in both groups rose significantly in the first half of gestation reaching a plateau in the second half. The α2‐antiplasmin levels remained constant in both groups, although the smokers started with significantly higher levels: 119 versus 105 % in the nonsmokers. The D‐dimer levels rose significantly in both groups: from 278 to 847 μg/ml in the nonsmokers and from 215 to 520 μg/ml in the smokers. They were significantly lower in the smoking group from the 11th up to the 40th weeks. The D‐dimer/TAT ratio was significantly higher in the nonsmokers. Conclusions In smoking pregnant women the activated coagulation process was not counterbalanced by an adequate increase of fibrinolysis which was the case in the nonsmokers.