Objective: To investigate the effects of an intense multicomponent intervention program among all pregnant smokers still smoking at the 18th week of pregnancy in two municipalities. Methods: A study at two hospitals in different counties of 212 pregnant women still smoking at the time of routine ultrasound screening examination at the 18th week of pregnancy. In the intervention group at one hospital, 107 women received monthly consultations with an obstetrician at the hospital (in addition to the routine pregnancy care program taken care of by general practitioners). Verbal and written information on the detrimental effects of smoking, assessment of daily smoking habit confirmed by the measurement of expirational carbon monoxide (CO), counseling on behavioral strategies on how to quit or reduce smoking, and an ultrasound examination to estimate the growth and biophysical score of the fetus was performed at each visit. In the neighboring county, 105 pregnant smokers registered in the same period received the standard pregnancy care program (taken care of by general practitioners) constituting the control group. The statistical analyses applied were variance analyses and chi(2) tests. Results: In the intervention group, 28% stopped smoking and 35% reduced smoking, whereas 26% did not change their smoking habit and 11% increased their consumption. This may be compared with the pregnant smokers in the neighboring county, receiving standard pregnancy care, among whom 11% stopped smoking, 49% reduced their consumption, 37% did not change their smoking habits, and 3% increased their daily smoking. The difference in smoking cessation is highly significant. However, the smoking cessation occurred mostly among light smokers (10 cigarettes or fewer daily). Relapse to daily smoking within 1 year after delivery was 100% in the intervention group and 66% in the standard pregnancy care group. Conclusions: This resource-demanding multicomponent intervention model does not seem to give additional benefits compared with other less demanding intervention models. Most of the quitters were light smokers, thus being at less risk.