Background: Hospitalists involved in perioperative care either stop or continue until the day of surgery renin-angiotensin-aldosterone system antagonists (either angiotensin-converting enzyme inhibitors [ACEI] or angiotensin II receptor subtype 1 antagonists [ARA]) in patients who use these agents chronically. This practice variation reflects uncertainty regarding the risks and benefits of either approach. Purpose: The purpose of this study was to assess the clinical consequences of preoperatively continuing versus withholding ACEI/ARAs in patients treated chronically with these agents. Data Sources and Study Selection: We comprehensively searched 7 major electronic databases, considered references from selected reviews, hand-searched journals, and communicated with experts. We included randomized trials and observational studies. Data Extraction: We evaluated the relative risk (RR) of hypotension requiring vasopressors and of myocardial infarction in patients who did or did not receive an immediate preoperative dose of ACEI or ARA. Data Synthesis: Random-effects meta-analysis from 5 studies totaling 434 patients suggested that patients receiving an immediate preoperative ACEI/ARA dose were more likely (RR 1.50, 95% CI 1.15-1.96) to develop hypotension requiring vasopressors at or shortly after induction of anesthesia. Sufficient data were not available to assess other outcomes. Conclusions: Preoperative administration of ACEI/ARAs increases intraciperative hypotension. The long-term clinical consequences of continuing versus withhold- ing preoperative ACEI/ARAs are unknown. This uncertainty stems in part from the absence to date of randomized trials designed specifically to examine patient-important consequences of this decision. © 2008 Society of Hospital Medicine.