OBJECTIVE:To estimate the prevalence of medicine use among high school students (14-18 years old) living in an urban area in Southern Brazil and the proportion who self-medicate and to explore the association between medicine use and demographic, socioeconomic, and behavioral variables.METHODS:A school-based survey was conducted among high school students in the city of Maringá/PR, Brazil in 2007. The sample students were selected through two-stage random sampling. The sample included 991 students (54.5% females) from eight public and four private high schools. The data were collected using a structured questionnaire. Only medications used within the 15 days preceding data collection were considered. The independent variables studied were sex, age, socioeconomic status, living with parents, employment status, smoking habits, and alcohol use.RESULTS:The prevalence of medicine use among the adolescents was 55.8% (females = 64.3%, males = 45.7%, p<0.001) and 52.6% of this use represented self medication (females = 51.0%, males = 56.8, p = 0.21). The factors associated with medicine use were age, employment, and smoking, while the factors associated with self medication were male gender and employment. Chronic users did not tend to self-medicate.CONCLUSION: The data from this study demonstrate a high prevalence of medicine use and self medication; however, the variables associated with medicine use and self medication differed. Urgent strategies to promote the rational use of drugs in this population and their families are necessary.