Background: Recurrent bleeding from an intracranial aneurysm after subarachnoid hemorrhage (SAH) is associated with unfavorable outcome. Recurrent bleeding before aneurysm occlusion can be performed occurs in up to one in five patients and most often happens within the first 6 h after the primary hemorrhage. Reducing the rate of recurrent bleeding could be a major factor in improving clinical outcome after SAH. Tranexamic acid (TXA) reduces the risk of recurrent bleeding but has thus far not been shown to improve functional outcome, probably because of a higher risk of delayed cerebral ischemia (DCI). To reduce the risk of ultraearly recurrent bleeding, TXA should be administered as soon as possible after diagnosis and before transportation to a tertiary care center. If TXA is administered for a short duration (i.e., < 24 h), it may not increase the risk of DCI. The aim of this paper is to present in detail the statistical analysis plan (SAP) of the ULTRA trial (ULtra-early TRranexamic Acid after Subarachnoid Hemorrhage), which is currently enrolling patients and investigating whether ultraearly and short-term TXA treatment in patients with aneurysmal SAH improves clinical outcome at 6 months. Methods/design: The ULTRA trial is a multicenter, prospective, randomized, open, blinded endpoint, parallel-group trial currently ongoing at 8 tertiary care centers and 16 of their referral centers in the Netherlands. Participants are randomized to standard care or to receive TXA at a loading dose of 1 g, immediately followed by 1 g every 8 h for a maximum of 24 h, in addition to standard care, as soon as SAH is diagnosed. In the TXA group, TXA administration is stopped immediately prior to treatment (coil or clip) of the causative aneurysm. Primary outcome is the modified Rankin Scale (mRS) score at 6 months after SAH, dichotomized into good (mRS 0-3) and poor (mRS 4-6) outcomes, assessed blind to treatment allocation. Secondary outcomes include case fatalities at 30 days and at 6 months and causes of poor clinical outcome. Safety outcomes are recurrent bleeding, DCI, hydrocephalus, per-procedural complications, and other complications such as infections occurring during hospitalization. Data analyses will be according to this prespecified SAP. Trial registration: Netherlands Trial Register, NTR3272. Registered on 25 January 2012. ClinicalTrials.gov, NCT02684812. Registered on 17 February 2016.