OBJECTIVES: Chronic disease therapies have to be taken for long periods, usually indefinitely; hence the risk of discontinuation is often high. Low compliance/persistence may compromise the potential benefits of treatment. The purpose of this study was to investigate patients' adherence and persistence to therapy with hypolipemic medications using a large administrative database. METHODS: We used the Regione Lombardia Health Service (RLHS) administrative databases, which contain information on a population of >9 millions individuals with universal healthcare and pharmaceutical coverage. The study population included individuals with at least one prescription of a hypolipemic agent during the year 2003 and who were enrolled in the RLHS in the year 2003. Persistence and adherence was evaluated with the medication possession ratio (MPR), calculated as the ratio between the number of pills dispensed during the study period and the number of days of observation. MPR was estimated for individuals who filled their first prescription in the year before 31 October 2003. RESULTS: Out of a population of 9,108,645 members, 560,737 (6.2%) received at least one prescription of a study drug. Frequency of use increased from 0.7% in subjects with age <40 years to 18.4% in subjects age 70-79 y.o.. A total of 16.2% of subjects received one or two packs during the study period, the median number of packs prescribed was 14, and simvastatin (35.4%), atorvastatin (27.6%) and pravastatin (13.2%) were the most prescribed initial drugs. A total of 503,023 patients were considered for the adherence analysis: 34.9% of subjects had MPR<0.4; 34.7% between 0.4 and 0.8; and 30.4%>0.8. CONCLUSION: Persistent and adherence with hypolipemic medications is far from optimal in this large cohort of subjects. This phenomenon is common to many asymptomatic chronic therapies and deserves further investigations, as it indicates that a relevant part of drug resources are spent without a predictable clinical benefit.