BACKGROUND AND PURPOSE: Arterial reocclusion and distal embolization are known complications of ischemic stroke intervention, impacting treatment strategies and device design. We sought to determine their rates of occurrence and effects on long-term outcomes during endovascular treatment of patients with acute ischemic stroke. MATERIALS AND METHODS: Retrospective analysis of data from 4 prospective acute stroke protocols was performed. Patients underwent the standard technique for parent vessel angiography followed by pharmacologic thrombolysis and/or sonographic thrombolysis and/or mechanical thrombus disruption. Certain patients also received systemic heparin or abciximab therapy. Demographic, clinical, and angiographic variables were assessed at onset, 24 hours, 1 week, and 1-3 months after the event. "Distal embolization" was defined qualitatively as appearance of an occlusion on a downstream vessel. "Arterial reocclusion" was defined as subsequent reocclusion of the target vessel after initial recanalization had been achieved. RESULTS: Arterial reocclusion occurred in 18% of these patients, whereas distal embolization occurred in 16% of the 91 patients treated in these protocols. Arterial reocclusion, but not distal embolization, was associated with a lower likelihood of favorable outcome at 1-3 months (P = .05; odds ratio, 3.9; 95% confidence interval, 0.01-0.98) after adjusting for age, initial National Institutes of Health Stroke Scale scores, sex, time to treatment, initial angiographic grade, symptomatic intracranial hemorrhage, and final recanalization. CONCLUSIONS: Arterial reocclusion and distal embolization occur in 16%-18% of patients with stroke undergoing endovascular intervention. Only arterial reocclusion is associated with poor long-term outcome. Prospective studies are needed to identify risk factors for their occurrence and possible preventive therapies.