Etretinate has been detected in the blood of women taking acitretine. Because of the proven teratogenic effects of etretinate it was decided to try to trace all users of acitretine in The Netherlands via all drug dispensing outlets (1450 community pharmacies, 95 hospital pharmacies and 636 general practitioners). A request for information on the date of birth, sex, type of prescriber, and the number of capsules dispensed yielded a response rate of 87%. In 61% of all the responding dispensing outlets a prescription for acitretine had been filled. Of these 1153 outlets, 40% had dispensed acitretine to one patient and 52% had dispensed it to 2-5 patients. The 2717 patients comprised 1500 men (55%) and 1217 women, with mean ages of 48 and 53 y, respectively. As against 45% of all the male users, 31% of all the women were in the child-bearing age (15-45 y). The average numbers of dispensed capsules was 167 to users of 10 mg capsules, and 107 to users of the 25 mg capsules. In more than 80% of cases acitretine had been prescribed by dermatologists. Because the large majority of inhabitants in The Netherlands use one community pharmacy, and because most of them have automated records, it is possible to trace a cohort of users quickly and almost completely. Because most large-scale problems with adverse reactions are discovered within the first 2 years of marketing, at a time when exposure and morbidity registries are still collecting information, adhoc formation of a cohort in this way may be a useful resource for postmarketing surveillance.