Protease inhibitor-based antiretroviral therapy has been shown to decrease the morbidity and mortality associated with human immunodeficiency virus type 1 (HIV-1) infection. However, many of the available agents in this class suffer shortcomings, including poor tolerability, difficult dosing regimens, and variable drug concentrations which may lead to generation of viral resistance. Lopinavir/ritonavir (Kaletra) has been designed specifically to address some of these shortcomings. Excellent therapeutic efficacy has been documented for lopinavir/ritonavir in multiple clinical trials in both antiretroviral-naive and -experienced patients. Development of resistance is a rare event in persons initiating therapy with lopinavir/ritonavir as their first protease inhibitor. The main side effects associated with lopinavir/ritonavir are gastrointestinal disturbances and elevations of serum lipids. Current antiretroviral therapy guidelines list lopinavir/ritonavir as the consensus first-line protease inhibitor recommended in the initial therapeutic regimen in persons infected with HIV-1.