The aim of this study was to evaluate the prevalence and causative factors associated with self-medication in the elderly and identify the main drugs consumed without prescription. A cross-sectional population-based study with stratified clustered two-stage sampling was performed in Campinas, Sao Paulo, Brazil in 2008 and 2009. Of the 1,515 elderly studied, 80.4% reported using at least one drug during the three days preceding the survey. Of these, 91.1% reported the use of prescription drugs only and the remainder (8.9%) reported simultaneous use of prescribed and non prescribed drugs. After adjustment, a negative association between age >= 80 years, hypertension, chronic diseases, use of health services, dental consultations and adherence to a medical plan, and self-medication was found, whereas a positive association was found with per capita income. Dipyrone, acetylsalicylic acid, diclofenac, Ginkgo biloba, paracetamol and homeopathic medicines were among the most used non-prescribed drugs. Pharmaceutical assistance should be provided as a priority to the elderly, to avoid the misuse of medicines and ensure access to the correct drugs.282335345