Although human immunodeficiency virus (HIV) protease inhibitors (PIs) improve survival in patients with HIV infection, many patients receiving PIs develop hyperlipidemia, which may increase risk of future coronary events. The purpose of this study was to estimate the changing prevalence of lipid-lowering therapy (LLT) in patients with HIV and to evaluate its association with the use of HIV PIs. This was a cross-sectional study of adults with HIV infection who were registered in the Medicaid of California (MEDI-CAL) administrative claims database. Frequencies of HIV-related and dyslipidemia diagnoses were determined from International Classification of Diseases-9th Edition codes. Use of lipid-lowering and antiretroviral medications was determined by National Drug Codes. Multivariate statistical techniques were used to evaluate trends in use of PIs and lipid-lowering medications from January 1996 to June 2002. The number of HIV-infected patients in MEDI-CAL ranged from 15,764 in 1996 to 13,349 in 2000. The prevalence of LLT use among HIV-infected patients on PIs increased by sixfold (1.7% to 10.6%, p <0.05), and in 2000, exceeded use in the overall MEDI-CAL population (p = 0.09). The increasing rate of LLT in patients taking PIs was greater than in HIV-infected patients not on PIs and in MEDI-CAL (p = 0.002). In multivariate models, increasing age (odds ratio 2.30) and use of PIs (odds ratio 2.08) predicted use of LLT (p <0.001). Thus, in patients taking HIV PIs, use of LLT increased more than sixfold, at a faster rate than in the general population. It has not been proved that use of LLT in HIV-infected patients taking PIs improves survival.