Background: Little is known regarding functional outcome following poor-grade (World Federation of Neurosurgical Societies grades IV and V) aneurysmal subarachnoid hemorrhage (aSAH), especially in individuals treated aggressively in the early phase after ictus. Methods: We provided patients with aSAH with ultra-early definitive treatment, coiling or clipping, within 6 hours from arrival as per protocol. We classified the patients into 3 groups according to their computed tomography findings: Group 1, intraventricular hemorrhage with obstructive hydrocephalus; Group 2, massive intracerebral hemorrhage with brain herniation; and Group 3, neither Group 1 nor Group 2. We retrospectively evaluated patients with poor-grade aSAH who were admitted to our department between January 2013 and December 2016. We evaluated functional outcome at 6 months, defining modified Rankin Scale (mRS) scores of 0-2 as good and those of 3-6 as poor outcomes. Results: A good functional outcome was observed in 39.4% (28/71) of all cases. All-cause mortality at 6 months was 15.5% (11/71). A good outcome in Group 3 was significantly higher than that in the other two groups (Group 1 and 2 vs. Group 3, 20.8% vs. 48.9%, p = 0.02), even after adjustment with a multiple logistic regression analysis (odds ratio 6.1, 95% confidence interval 1.1 to 34.8). Conclusions: Approximately 40% of patients with poor-grade aSAH became functionally independent, and approximately half of the patients with poor-grade aSAH who had neither intraventricular hemorrhage with obstructive hydrocephalus nor with brain herniation had good functional outcomes. Although further trials are required to confirm our results, ultra-early surgery may be considered for patients with poor-grade aSAH.