Purpose To evaluate the effectiveness of mechanical thrombectomy with the use of a stent retriever in acute ischemic stroke, performed by using a balloon guide catheter or non-balloon guide catheter. Materials and Methods In accordance with the institutional review board approval obtained at the two participating institutions, retrospective analysis was performed in 183 consecutive patients treated between 2013 and 2014 for occlusions in the middle cerebral artery or carotid terminus by using a stent retriever with a balloon guide catheter (n = 102) at one center and a non-balloon guide catheter (n = 81) at the other center. Data on procedure duration, number of passes, angiographic findings, type of stent retriever used, and expertise of the operators were collected. Successful recanalization was defined as grade 3 or 2b modified Treatment in Cerebral Ischemia recanalization accomplished in up to three passes. Univariate and multivariate subgroup analyses were conducted to control for the confounding variables of prior thrombolysis, location of occlusion, and operator expertise. Results Successful recanalization with the balloon guide catheter was achieved in 89.2% of thrombectomies (91 of 102) versus 67.9% (55 of 81) achieved with the non-balloon guide catheter (P = .0004). The one-pass thrombectomy rate with the balloon guide catheter was significantly higher than for that with the non-balloon guide catheter (63.7% [65 of 102] vs 35.8% [29 of 81], respectively; P = .001). The procedure duration was significantly shorter by using the balloon guide catheter than the non-balloon guide catheter (median, 20.5 minutes vs 41.0 minutes, respectively; P < .0001). Conclusion The effectiveness of mechanical thrombectomy with stent retrievers in acute ischemic stroke in the anterior circulation in terms of angiographic results and procedure duration was improved when performed in combination with the balloon guide catheter. (©) RSNA, 2016.