BACKGROUND:Polypharmacy and potentially inappropriate medication (PIM) are associated with adverse outcomes such as hospitalization, loss of productivity, and death. OBJECTIVE:This study evaluates the prevalence of polypharmacy and PIM in the adult community-dwelling population in Switzerland. METHODS:The analysis is done based on claims data from the largest health insurance in Switzerland. We calculated the number of medications submitted for reimbursement, the proportion of persons with polypharmacy, and the proportion of persons receiving PIM according to the 2003 Beers criteria and the PRISCUS list. Additionally, we estimated cost for medications and PIM, and identified the most prevalent groups of PIM according to the Anatomical Therapeutic Chemical Classification System (ATC). RESULTS:17 % of the adult community-dwelling population in Switzerland received 5 or more medications which is one of the common definitions of polypharmacy, and over 21 % of adults aged more than 65 years had a PIM according to 2003 Beers criteria or the PRISCUS list. The most prevalent classes of PIM were psycholeptics, sex hormones, psychoanaleptics, and antiinflammatory drugs. CONCLUSION:Although the present study has a number of limitations, we conclude that the prevalence of polypharmacy and PIM in Switzerland is high. A broad spectrum of interventions on the individual level as well as on the population level is urgently needed.