BackgroundTo investigate whether collateral status could modify the associations between post‐thrombectomy blood pressure (BP) measures and outcomes.Methods and ResultsPatients with anterior‐circulation large‐vessel‐occlusion successfully recanalized in a multicenter endovascular thrombectomy registry were enrolled. Pretreatment collateral status was graded and dichotomized (good/poor) in angiography. Maximum, minimum, and mean systolic BP (SBP) and BP variability (assessed by the SD, coefficient of variation) during the initial 24 hours after endovascular thrombectomy were obtained. The primary outcome was unfavorable 90‐day outcome (modified Rankin Scale score 3–6). Secondary outcomes included symptomatic intracranial hemorrhage and 90‐day mortality. Adjusted odds ratios (aOR) of BP parameters over the outcomes were obtained in all patients and in patients with good/poor collaterals. Among 596 patients (mean age 66 years; 59.9% males), 302 (50.7%) patients had unfavorable 90‐day outcome. In multivariable analyses, higher mean SBP (aOR, 1.59 per 10 mm Hg increment; 95% CI, 1.26–2.02;P<0.001), mean SBP >140 mm Hg (versus ≤120 mm Hg; aOR, 4.27; 95% CI, 1.66–10.97;P=0.002), and higher SBP SD (aOR, 1.08 per 1‐SD increment; 95% CI, 1.01–1.16;P=0.02) were respectively associated with unfavorable 90‐day outcome in patients with poor collateral but not in those with good collateral. A marginal interaction between SBP coefficient of variation tertiles and collaterals on 90‐day functional outcome (Pfor interaction, 0.09) was observed. A significant interaction between SBP coefficient of variation tertiles and collaterals on 90‐day mortality (Pfor interaction, 0.03) was observed.ConclusionsHigher postprocedural BP is associated with 90‐day unfavorable outcomes after successful endovascular thrombectomy in patients with poor collateral.RegistrationURL:https://www.chictr.org.cn; Unique identifier: ChiCTR1900022154.