Aneurysmal subarachnoid hemorrhage (SAH) is a fatal disease with high morbidity and mortality. While the primary injury results from the initial bleeding and cannot be influenced, secondary injury through vasospasms and delayed cerebral ischemia (DCI) during the course of the disease might be a target for intervention in order to improve outcome. To date, beside the aneurysm treatment to prevent re-bleeding and the administration of oral nimodipine, there is no causal therapy available, so that novel treatment concepts are desperately needed. There are strong indications that inflammation contributes to DCI and therefore poor outcome and plays a major role in SAH. Some studies suggest a beneficial effect of anti-inflammatory drugs like glucocorticoids (GC) in SAH patient, but there are no data from randomized controlled trials proving or disproving the beneficial effect of GC, so that current guidelines do not recommend the use of GC in SAH so far. This multi-center trial aims to generate the first confirmatory data in a controlled randomized fashion that dexamethasone (DEX) improves the outcome in a clinically relevant endpoint in SAH patients. Moreover, this trial will generate first data in a secondary analysis, whether the initial inflammatory state of SAH patients defines a subgroup that particularly responds to a treatment with DEX.