Information on chronic drug use at any time in the past was collected with a self-administered questionnaire as part of a prospective cohort study on diet, other life-style factors and cancer among subjects aged 55-69 years. The validity of the questionnaire information on drug use was evaluated among 207 subjects by comparing it to pharmacy records of dispensed drugs. The comparison could be made for the 2.5-year period preceding the questionnaire administration. Since the study subjects did not mention prescription drugs that were not dispensed by their pharmacy, indicating no errors of commission, the analyses were focused on the estimation of sensitivity of drug recall and its correlates. Questionnaire recall of drug use amounted overall to 61.2% of drugs prescribed to the subjects for at least 6 months. Drug recall decreased with increasing age and with increasing number of prescribed chronic use of drugs per subject. No difference in recall was observed between men and women. Recall tended to improve with increasing duration of use and varied with type of drug. When only long-term drug use at the time of questionnaire administration was considered, overall recall of drug use was 68.8%.