BACKGROUND: The validity of children's self-reports on medicine use has not been reported. OBJECTIVE: To determine the agreement between parents' and children's reports of medicine use for 5 common complaints and to analyze predictors for disagreement. METHODS: We used the child-parent validation survey from the research project Health Behaviour in School-Aged Children. Three hundred ninety-three 11- and 13-year-old Danish children and their parents responded to identical questionnaires. The main outcome measures were self-reported medicine use during the previous month for headache, stomachache, difficulties in falling asleep, nervousness, and asthma. RESULTS: The percent agreement was lowest with medicine use for headache (64.6%), but was very high for the other 4 complaints (85.3-91.8%). The simple kappa coefficients were moderate to good for medicine use for headaches, stomachache, and asthma (0.31-0.58) but poor for difficulties in falling asleep and nervousness. Children who had the specific complaint during the previous month were more likely than their parents to report more frequent medicine use. CONCLUSIONS: We have some confidence in young adolescents' self-reports of medicine use, as the results of this study are in keeping with other studies on the validity of children's reports of health-related behaviors. Furthermore, the findings suggest that such data can be used in epidemiologic studies that aim to categorize children into groups with and without medicine use.