Purpose: Clinically successful endovascular therapy (EVT) in ischemic stroke requires reliable noninvasive pretherapeutic selection criteria. We investigated the association of imaging parameters including CT angiographic collaterals and degree of reperfusion with clinical outcome after EVT. Methods: In our database, we identified 93 patients with large vessel occlusion in the anterior circulation treated with EVT. Besides clinical data, we assessed the baseline Alberta Stroke Program Early CT score (ASPECTS) on noncontrast CT (NCCT) and CT angiography (CTA) source images, collaterals (CT-CS) and clot burden score (CBS) on CTA and the degree of reperfusion after EVT on angiography. Three readers, blinded to clinical information, evaluated the images in consensus. Data-driven multivariable ordinal regression analysis identified predictors of good outcome after 90 days as measured with the modified Rankin Scale. Results: Successful angiographic reperfusion (OR 26.50; 95%-CI 9.33–83.61) and good collaterals (OR 9.69; 95%-CI 2.28–59.27) were independent predictors of favorable outcome along with female sex (OR 0.35; 95%-CI 0.14–0.85), younger age (OR 0.88; 95%-CI 0.83–0.92) and higher NCCT ASPECTS (OR 2.54; 95%-CI 1.01–6.63). Outcome was best in patients with good collaterals and successful reperfusion, but there was no statistical interaction between collaterals and reperfusion. Conclusions: CTA-collateral status was the strongest pretherapeutic predictor of favorable outcome in ischemic stroke patients treated with EVT. CTA-collaterals are thus well suited for patient selection in EVT. However, the independent effect of reperfusion on outcome tended to be stronger than that of CTA-collaterals.