We examined the possibilities of improving the retrospective collection of data on drug use during pregnancy. The European Registration of Congenital Anomalies (EUROCAT) has registered information on maternal drug exposure in the northern Netherlands through a question on the notification form for the registration of birth defects, filled out by physicians or midwives since 1981. Furthermore, hospital records are used and general practitioners are asked to add information on drug use. The present pilot study used pharmacy records and maternal questionnaires as well as maternal interview data to complete the data on drug exposure in the EUROCAT registration. Combined information from pharmacies, questionnaires, and interviews with the mother were used as the reference standard. Pharmacy records provided detailed data on 57% of drugs used (prescription drugs, mainly). Mothers were able to report 76% of drug groups used, but when only data on the exact name of the drug were studied, this figure was 52%. Of the drugs dispensed by the pharmacy, 6% were not used (false positives). We conclude that pharmacy records and maternal interviews are both indispensable sources of information on maternal drug exposure that provide much added value.