Inclusion of HIV protease inhibitors (PIs) in the treatment of people living with HIV+ has markedly decreased mortality but also increased the incidence of metabolic abnormalities, causes of which are not well understood. Here, we report that insulinopenia is exacerbated when Zucker fa/fa rats are exposed to a PI for 7 wk, suggesting that chronic PI exposure adversely affects pancreatic islet β-cell function. In support of this possibility, we find increased apoptosis, as reflected by TUNEL fluorescence analyses, and reduced insulin-secretory capacity in insulinoma cells and human pancreatic islet cells after in vitro exposures (48-96 h) to clinically relevant PIs (ritonavir, lopinavir, atazanavir, or tipranavir). Furthermore, pancreatic islets isolated from rats administered an HIV-PI for 3 wk exhibit greater cell death than islets isolated from vehicle-administered rats. The higher incidence of HIV-PI-induced cell death was associated with cleavage and, hence, activation of caspase-3 and poly(ADP)-ribose polymerase but not with activation of phospho-pancreatic endoplasmic reticulum (ER) kinase or induction of ER stress apoptotic factor C/EBP homologous protein. Exposure to the HIV-PIs, however, led to activation of mitochondria-associated caspase-9, caused a loss in mitochondrial membrane potential, and promoted the release of cytochrome c, suggesting that HIV-PIs currently in clinically use can induce β-cell apoptosis by activating the mitochondrial apoptotic pathway. These findings therefore highlight the importance of considering β-cell viability and function when assessing loss of glycemic control and the course of development of diabetes in HIV+ subjects receiving a protease inhibitor. Copyright © 2009 the American Physiological Society.