The ULTRA trial showed that ultra-early and short-term tranexamic acid treatment after subarachnoid hemorrhage did not improve clinical outcome at 6 months. An expected proportion of the included patients experienced nonaneurysmal subarachnoid hemorrhage. In this post hoc study, we will investigate whether ultra-early and short-term tranexamic acid treatment in patients with aneurysmal subarachnoid hemorrhage improves clinical outcome at 6 months. The ULTRA trial is a multicenter, prospective, randomized, controlled, open-label trial with blinded outcome assessment, conducted between July 24, 2013, and January 20, 2020. After confirmation of subarachnoid hemorrhage on noncontrast CT, patients were allocated to either ultra-early and short-term tranexamic acid treatment with usual care or usual care only. In this post hoc analysis, we included all ULTRA participants with a confirmed aneurysm on CT angiography and/or digital subtraction angiography. The primary endpoint was clinical outcome at 6 months, assessed by the modified Rankin scale (mRS), dichotomized into good (0-3) and poor (4-6) outcomes. Of the 813 ULTRA trial patients who experienced an aneurysmal subarachnoid hemorrhage, 409 (50%) were assigned to the tranexamic acid group and 404 (50%) to the control group. In the intention-to-treat analysis, 233 of 405 (58%) patients in the tranexamic acid group and 238 of 399 (60%) patients in the control group had a good clinical outcome (adjusted odds ratio aOR 0.92; 95% CI 0.69-1.24). None of the secondary outcomes showed significant differences between the treatment groups: excellent clinical outcome (mRS 0-2) (aOR 0.76; 95% CI 0.57-1.03), all-cause mortality at 30 days (aOR 0.91; 95% CI 0.65-1.28), and all-cause mortality at 6 months (aOR 1.10; 95% CI 0.80-1.52). Ultra-early and short-term tranexamic acid treatment did not improve clinical outcomes at 6 months in patients with aneurysmal subarachnoid hemorrhage and therefore cannot be recommended. ClinicalTrials.gov (NCT02684812; submission date February 18, 2016, first patient enrollment on July 24, 2013). This study provides Class II evidence that tranexamic acid does not improve outcomes in patients presenting with aneurysmal subarachnoid hemorrhage.