OBJECTIVES: We sought to 1) estimate the occurrence of polypharmacy, 2) define characteristics of patients most at risk for polypharmacy, and 3) characterize drug classes most commonly involved in polypharmacy in elderly patients in the Local Health Unit (LHU) of Parma, Italy. METHODS: We conducted a retrospective analysis of the 2007 Parma LHU automated outpatient prescriptions database. A total of 97,043 patients ≥65 years (94.2% of the cohort) who had at least one prescription medication were included in the study. Using the World Health Organization's Defined Daily Dose (DDD) to determine the duration of treatment for a given drug, we defined a polypharmacy episode as overlapping treatment with five or more drugs occurring at least one day during the study period. RESULTS: A total of 37,789 elderly in the population (38.9%) were exposed to at least one polypharmacy episode. The prevalence of polypharmacy substantially increased with age; 45.5% and 46.8% of individuals, respectively, in the 75-84 age group and 85 years and older were exposed to polypharmacy. For the exposed to polypharmacy, the median number of days of exposure was 55 and 14.8% were exposed for more than 200 days. Compared to the unexposed elderly, subjects exposed to polypharmacy were older, were prevalently male, and had a greater number of chronic conditions. Cardiovascular, gastrointestinal and metabolism, and blood medications were most commonly involved in polypharmacy. CONCLUSIONS: Polypharmacy is widespread among the elderly. LHU managers should develop educational activities to make general practitioners aware of the magnitude of polypharmacy phenomenon among their elderly patients. In addition, LHU and clinicians should jointly identify strategies to closely monitoring elderly patients more likely to be exposed to polypharmacy.