Background and aims Smoking in pregnancy significantly increases the risk of preterm birth and fetal growth restriction. Pregnant women are encouraged to quit smoking. Smoking in general is discouraged by antismoking laws. In the present study, we describe trends in smoking in pregnancy in the Netherlands for 2001–2010. Methods National surveys in 2001, 2002, 2003, 2005, 2007, and 2010. In well baby clinics, questionnaires were handed out to mothers with infants ≤ 6 months. Results Out of a total number of 28,720 questionnaires, 16,358 (57%) were returned. Between 2001 and 2010, prevalence of smoking in pregnancy dropped by half; from 13.0% in 2001 to 6.3% in 2010 (P trend < 0.001). The odds of being a smoker was 6.3 (95%CI 5.3–7.4) for mothers with a low education level, and 3.0 (95% CI 2.5–3.5) for mothers with a medium education level, as compared to mothers with high education level. Independently of their educational level, mothers smoked on average five cigarettes per day while pregnant. We observed a sharp decrease in prevalence of smoking in pregnancy from 2003 to 2005 among women with a medium or a high education level. An almost continuous, downward trend was seen among mothers with a low level education. The 2003–2005 decrease coincided with the implementation of antismoking laws in the Netherlands. Conclusions Between 2001 and 2010, prevalence of smoking in pregnancy dropped by half. But still, in 2010, 6.3% of Dutch pregnant women were smokers, exposing about 11,000 unborn children per year to significantly increased health risks.