We studied the relationship between the timing of discontinuing chronic angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor subtype 1 antagonists (ARA) and hypotension after the induction of general anesthesia in a general surgical population. We retrospectively studied 267 hypertensive patients receiving chronic ACEI/ARA therapy undergoing elective noncardiac surgery under general anesthesia. During preoperative visits, patients were asked to either take their last ACEI/ARA therapy on the morning of surgery or withhold it up to 24 h before surgery. The number of hours from the last ACEI/ARA dose to surgery was recorded during the preoperative interview. Electronic medical and anesthesia records were reviewed for comorbidities, type and dose of anesthetics used, intraoperative hemodynamics, IV fluids, perioperative vasopressor administration, and rate of severe postoperative complications. Arterial blood pressure (BP) and heart rate were recorded during the 60-min postinduction period, and hypotension was classified as moderate (systolic BP <or=85 mm Hg) and severe (systolic BP <or=65 mm Hg). We analyzed all variables separately for patients who took their last ACEI/ARA therapy <10 h and >or=10 h before surgery. During the first 30 min after anesthetic induction, moderate hypotension was more frequent in patients whose most recent ACEI/ARA therapy was taken <10 h (60%) compared with those who stopped it >or=10 h (46%) before induction (P = 0.02). The adjusted odds ratio for moderate hypotension was 1.74 (95% confidence interval, 1.03-2.93) for those who took their ACEI/ARA therapy <10 h before surgery (P = 0.04). There were no differences between groups in the incidence of severe hypotension, nor was there a difference in the use of vasopressors. During the 31-60 min after induction, the incidence of either moderate (P = 0.43) or severe (P = 0.97) hypotension was similar in the two groups. No differences in postoperative complications were found between groups. In conclusion, discontinuation of ACEI/ARA therapy at least 10 h before anesthesia was associated with a reduced risk of immediate postinduction hypotension.