The outcome of patients with aneurysmal subarachnoid hemorrhage (SAH) has improved slowly over the past 25 years. This improvement may be due to early aneurysm repair by endovascular or open means, use of nimodipine, and better critical care management. Despite this improvement, mortality remains at about 40%, and many survivors have permanent neurologic, cognitive, and neuropsychologic deficits. Randomized clinical trials have tested pharmacologic therapies, but few have been successful. There are numerous explanations for the failure of these trials, including ineffective interventions, inadequate sample size, treatment side effects, and insensitive or inappropriate outcome measures. Outcome often is evaluated on a good-bad dichotomous scale that was developed for traumatic brain injury 40 years ago. To address these issues, we established the Subarachnoid Hemorrhage International Trialists (SAHIT) data repository. The primary aim of the SAHIT data repository is to provide a unique resource for prognostic analysis and for studies aimed at optimizing the design and analysis of phase III trials in aneurysmal SAH. With this aim in mind, we convened a multinational investigator meeting to explore merging individual patient data from multiple clinical trials and observational databases of patients with SAH and to create an agreement under which such a group of investigators could submit data and collaborate. We welcome collaboration with other investigators.