Introduction: To investigate the risk factors affecting the prognosis of elderly patients with severe aneurysmal subarachnoid hemorrhage (aSAH). Methods: Forty-nine elderly patients with severe aSAH (Hunt and Hess [H-H] grade III–V) were enrolled in this retrospective study. Follow-up was conducted with patients 30 days after discharge using the Glasgow Outcome Scale (GOS), on which scores of 1–3 indicated a poor outcome (n = 32) and scores of 4–5 indicated a good outcome (n = 17). The patients’ general information (gender, age, presence of hypertension, diabetes, or coronary atherosclerotic heart disease, location of ruptured aneurysm, and H-H grade) and complications (cerebral vasospasm, new cerebral infarction, pulmonary infection, liver dysfunction, hypoalbuminemia, anemia, and electrolyte disturbance) were recorded, and comparison between the different outcome groups was undertaken. Univariate analysis was used to analyze the factors associated with different outcomes, and multivariate logistic regression analysis was used to determine the factors that lead to poor outcomes. Results: The incidence of all complications increased in patients with higher H-H grades, but without statistical significance (P > 0.05). There was no statistically significant difference between the two outcome (poor and good) groups in general information and complications (all P > 0.05), with the exception of different H-H grades (P < 0.05). H-H grade was a statistically significant risk factor for poor outcomes in elderly patients with severe aSAH (OR 11.627, 95% CI 2.475–55.556, P = 0.002). Conclusion: H-H grade is an independent factor related to the prognosis of elderly patients with severe aSAH. © 2020, Springer Healthcare Ltd., part of Springer Nature.