Purpose: To study the prevalence of prescribed and over-the-counter (OTC) medicine use in children under 12 years of age in Finland and to examine factors associated with the medicine use. Methods: A nationwide population survey was carried out in Finland in spring 2018 with a random sample of children under 12 years (n = 8000). A response rate of 24% (n = 1921) was attained. The questionnaire was sent to the child's primary guardian. Current use of prescribed medicines and the use of OTC medicines in the preceding 2 days were the main outcome measures. Results: Of all the children 19% had used prescribed medicines, 15% OTC medicines, and 31% either prescription or OTC medicines during the preceding 22 days. Children's health related factors were positively associated with prescribed medicine use including fairly good to poor health status, symptoms experienced, and illnesses diagnosed by a physician. The guardian's healthcare education and use of prescribed medicines were also associated with children's prescribed medicine use. Symptoms of illnesses and fairly good health status were found to be associated with childrens' use of OTC medicines. Conclusions: The use of medicines in children under 12 years of age is quite common in Finland. As expected, children's health-related factors were associated with medicine use. Also, guardians' healthcare education and the use of prescribed medicines were associated with children's prescription medicine use. Children's medicine use should be continuously monitored and investigated further to identify the reasons leading to appropriate and inappropriate medicine use in children. K E Y W O R D S child, medicine use, over-the-counter medicines, prescribed medicines, survey Key Points • One in five children under 12 years in Finland used prescribed medicines and one in seven over-the-counter (OTC) medicines.