Objective. To establish the prevalence of chronic diseases reported by parents among a random population of Dutch children. Furthermore, to establish how often these children visited a physician because of a chronic disease, and used drugs for its treatment. Setting. Dordrecht and environs. Design. Descriptive. Method. In the school year 1990-1991, all 8689 parents of school children summoned for a periodical health check by the school doctor or school nurse were sent a questionnaire together with the notification. With the aid of a list of criteria it was determined for every child during the periodical health check if the diseases, if any, were serious, if the children were being treated for them and if they used medication. Results. The response to the questionnaire amounted to 98.3%. Of the children examined, 21.3% according to the parents suffered from one or more chronic diseases, 3.7% to a major extent. Of the group with one or more chronic diseases, 25.2% were monitored by the family doctor, 10.5% by the paediatrician, 18.6% by various other specialists and 4.5% by a homeopathist. Of the population as a whole, 10.1% used medication because of one or several of the chronic diseases; this accounted for 47.4% of the group with one or several chronic diseases. Conclusion. The prevalence of chronic diseases in school children reported by the parents is so high that it should be given attention in post-graduate education and public health information.