OBJECTIVE: To study the dispensing of potentially teratogenic drugs in the 12-month period before as well as during pregnancy in the Netherlands. DESIGN: Population-based study. SETTING: A cohort was constructed using a linkage between the PHARMO Dtabase Network and the Netherlands Perinatal Registry (PRN). POPULATION: A total of 203 962 Dutch pregnancies reported between 1999 and 2007 METHODS: Drug-dispensing information was identified from the PHARMO Database Network for the 12-month period before conception and during pregnancy. Drugs with either a Swedish FASS ‘D’ classification, an Australian ADEC or American FDA ‘D’ or ‘X’ classification were considered potentially teratogenic (n = 202). MEAN OUTCOME MEASURES: Proportion of pregnancies thatreceived potentially teratogenic drugs in the 12-month period before and during pregnancy and specific for the risk category X drugs and newly initiated drugs. RESULTS: Sixteen percent of the pregnancies received a potentially teratogenic drug in the 12-month period before and 5.07% during pregnancy. Doxycycline and paroxetine were most frequently received during pregnancy by 1.01% and 0.85% of women, respectively; 0.66% of the women received a risk category X drug during pregnancy which most frequently consisted of triptorelin (0.25%), norethisterone (0.22%) and simvastatin (0.03%). Fifty-three percent of the women who received a potentially teratogenic drug during pregnancy received this for the first time during the study period. These percentageswere heterogeneous between therapeutic drug classes. CONCLUSIONS: Five percent of the pregnancies received a potentially teratogenic drug during pregnancy and 0.66% received a drug from the risk category X. It may be possible to reduce these proportionswhen reasons for prescription have been explored.