OBJECTIVE: To evaluate the outcomes of large or giant vertebrobasilar dissecting aneurysms (VBDAs) after endovascular total embolization by follow-up 3T magnetic resonance imaging (MRI). METHODS: Between November 2011 and July 2015, 4 patients had unruptured large or giant VBDAs that were treated with endovascular techniques with total embolization of VBDAs confirmed on follow-up angiography, but the patients had persistent or worsened symptoms. Preoperative and postoperative 3T high-resolution MRI was performed to evaluate arterial wall evolution. RESULTS: Follow-up angiographic results were satisfactory in all 4 patients; however, symptoms in cases 1, 2, and 4 worsened, and symptoms in case 3 did not improve. Postoperative high-resolution MRI in case 1 showed a new intramural hematoma, and postoperative high-resolution MRI of cases 2, 3, and 4 showed persistent intramural hemorrhagic signals. Follow-up MRI showed increased aneurysm size in cases 1, 2, and 4 but no size change in case 3. CONCLUSIONS: The efficacy of conventional endovascular treatment (e.g., internal trapping with coils, stent-assisted coiling, and stent placement without coils) for large or giant VBDAs is uncertain. Follow-up angiography alone does not adequately predict the outcome. High-resolution MRI is a worthwhile adjunct to follow these lesions.