Background Optimal definitive treatment timing for patients with aneurysmal subarachnoid hemorrhage (aSAH) remains controversial. We compared outcomes for aSAH patients with ultra-early treatment versus later treatment at a single large center. Method Patients who received definitive open surgical or endovascular treatment for aSAH between January 1, 2014, and July 31, 2019, were included. Ultra-early treatment was defined as occurring within 24 h from aneurysm rupture. The primary outcome was poor neurologic outcome (modified Rankin Scale score > 2). Propensity adjustment was performed for age, sex, Charlson Comorbidity Index, Hunt and Hess grade, Fisher grade, aneurysm treatment type, aneurysm type, size, and anterior location. Results Of the 1013 patients (mean SD age, 56 14 years; 702 69% women, 311 31% men) included, 94 (9%) had ultra-early treatment. Compared with the non-ultra-early cohort, the ultra-early treatment cohort had a significantly lower percentage of saccular aneurysms (53 of 94 56% vs 746 of 919 81%, P  <0 .001), greater frequency of open surgical treatment (72 of 94 77% vs 523 of 919 57%, P  <0 .001), and greater percentage of men (38 of 94 40% vs 273 of 919 30%, P  = .04). After adjustment, ultra-early treatment was not associated with neurologic outcome in those with at least 180-day follow-up (OR = 0.86), the occurrence of delayed cerebral ischemia (OR = 0.87), or length of stay (exp(β), 0.13) ( P  ≥ 0.60). Conclusions In a large, single-center cohort of aSAH patients, ultra-early treatment was not associated with better neurologic outcome, fewer cases of delayed cerebral ischemia, or shorter length of stay.