Lay summary – An acute subdural hematoma is a serious bleed between the brain and its outer covering that can happen after a traumatic brain injury. Some patients may need surgery to remove the blood and reduce pressure on the brain, while others may be treated without surgery using careful monitoring and supportive care. At present, it is not clear whether surgery leads to better outcomes than conservative treatment for most patients with this type of injury. More evidence is needed to help doctors decide which patients are most likely to benefit from surgery and which can be safely managed without it.