Objective:Before treatment for large and giant aneurysms, we need some of the predictors to prognose a good result. In this retrospective study, we attempted to determine criteria such as angiographic signs to identify good candidates for effective endovascular surgery.Methods:This study involved 45 patients with large or giant aneurysms treated by endovascular embolization. For angiographic study, we delivered a bolus injection of contrast medium. All aneurysms were confirmed angiographically and the morphology was defined in detail before endovascular embolization. We divided the patients into two groups based on angiographic findings. Group A (n = 16) manifested stasis of the contrast medium in the aneurysm on venous phase. Group B (n = 29) exhibited other findings. We retrospectively evaluated the relationship between stasis of the contrast medium in the aneurysm and results of endovascular embolization.Results and Discussion:There was no significant difference between the two groups with respect to the size of the aneurysm. However, the neck/dome ratio (P = 0·04) and size of the neck (P = 0·003) were significantly different between groups A and B. The morphological outcome was better in group A than group B (P = 0·03). We demonstrate that contrast stasis is a good predictor of outcome in patients with large or giant aneurysms to consider the endovascular embolization. Hemodynamic studies on large patient populations may reveal other factors predictive of a good treatment outcome.