Objective: To assess differences between native Spanish and immigrant pregnant women in behaviour relating to the use of medications during pregnancy. Study design: This crosssectional study was carried out at the department of obstetrics and gynaecology of an acute-care teaching hospital in the city of Barcelona, Spain. A total of 1103 women who gave birth at the hospital during a 1- year period were enrolled in the study. Each woman was interviewed by a gynaecologist during her stay in hospital after delivery, with special reference to drug use during the pregnancy. Drug exposure was assigned to trimesters, and drugs were divided into therapeutic groups, while the women taking part were divided up by nationality, educational level, parity and age. Data were analysed using bivariate, multivariate, and cluster analyses. Results: Slightly over half (55.7% ) of the women were native to Spain and 44.3% were immigrants of other nationalities. About a quarter, or 25.4% , of pregnant patients had not taken any drugs during their pregnancies. The most frequent drugs taken by the others were vitamins, which were used mostly by Spanish women, followed by analgesics, which were mostly taken by non-Spanish western women. The largest group who had taken folic acid was made up of non-Spanish western women, while the Asiatic patients had taken this in the smallest proportion of cases. Conclusions: Spanish patients and immigrants from other western countries showed a similar behaviour in terms of drug intake during pregnancy, which was different from the behavioural patterns seen in pregnant patients from developing countries. Objective: To assess differences between native Spanish and immigrant pregnant women in behavior relating to the use of medications during pregnancy. Study design: This crosssectional study was carried out at the department of obstetrics and gynaecology of an acute-care teaching hospital in the city of A total of 1103 women who gave birth at the hospital during a 1-year period were enrolled in the study. Each woman was interviewed by a gynaecologist during her stay in hospital after delivery, with special reference to drug use during the pregnancy. Drug exposure was assigned to trimesters, and the drugs were divided into therapeutic groups, while the women taking part were divided up by nationality, educational level, parity and age. Data were analysed using bivariate, multivariate, and cluster analyzes. Results: Slightly over half (55.7%) of the women were native to Spain and 44.3% were immigrants of other nationalities. About a quarter, or 25.4%, of pregnant patient The most frequent drugs taken by the others were vitamins, which were used mostly by Spanish women, followed by analgesics, which were mostly taken by non-Spanish western women. The largest group who had taken folic acid was made up of non-Spanish western women, while the Asiatic patients had taken this in the smallest proportion of cases. Conclusions: Spanish patients and immigrants from other western countries showed a similar behavior in terms of drug intake during pregnancy, which was different from the behavioral patterns seen in pregnant patients from developing countries.