OBJECTIVE: The number needed to treat to achieve the mortality benefit of HMG-CoA reductase inhibitors (statins) is substantially lower for secondary prevention populations when compared to primary prevention populations. To determine whether patients with "most to gain" are more compliant, we compared statin compliance in primary and secondary prevention populations in a midwestern managed care organization. METHODS: Non-Medicaid MCO enrollees who filled =2 statin prescriptions from January 1998 to November 2001 were included. Administrative data classified patients as secondary prevention (diagnosis of AMI or had undergone PTCA or CABG) or primary prevention (all others). Compliance was assessed by quantifying the number of days without medication (cumulative multiple refill-interval gap [CMG]) for 2 periods: 1) while actively taking statin (until last filled prescription ends), and 2) until termination (MCO termination, change to non-statin antihyperlipidemic, or end of observation period). RESULTS: Of 4,964 enrollees who received =2 statin prescriptions, 540 (11%) patients were classified as secondary prevention and 4424 (89%) primary prevention. The mean CMG while actively taking statin was 20.5% (SD 21.5, median 12.7) for the primary group and 21.9% (SD 22.7, median 13.3) for the secondary group (p=0.34). The mean CMG until termination was 29.2% (SD 26.9, median 20.1) and 31.5% (SD 27.3, median 24.6) for the primary and secondary groups respectively (p=0.06). Additional analyses will measure the effect of patient demographics, copayments, and prescriber specialty. CONCLUSIONS: Compliance with statins was similar and sub-optimal in primary and secondary prevention populations. These data demonstrate that patients exhibit poor compliance while actively taking therapy and contribute to future risk by discontinuing therapy at undesirable rates. While universal compliance with prescribed therapy for all patients indicated for therapy is a desirable goal, incremental efforts should aim at improving compliance in those populations who are the most likely to benefit from their use.