BACKGROUND: The Veterans Health Administration (VHA) develops guidelines for VHA providers that delineate specific criteria for use of certain complex, costly medications indicated for specialized populations. These criteria are disseminated to all VHA facilities. OBJECTIVE: To (a) assess the concordance with VHA guidelines for use of 4 antiretrovirals (atazanavir, darunavir, enfuvirtide, and tipranavir), and (b) to describe prescribing of these agents before and after implementation of the guideline criteria. METHODS: In this retrospective cohort study, we evaluated all veterans in VHA care who received their first outpatient prescription for a target antiretroviral between its FDA approval date and December 31, 2007, using outpatient prescription records obtained from the VHA Human Immunodeficiency Virus (HIV) Clinical Case Registry (CCR:HIV), an observational registry database created through extraction of specific clinical data from the VHA's electronic medical record. Adherence to the VHA guideline c...