Subdural hemorrhage (SDH) is bleeding around the brain coverings, specifically under a thick layer called dura but external to the brain and its immediate thinner layer, the arachnoid membrane. It results from tearing of blood vessels that travel between these layers. Acute treatment can be surgical draining or conservative close monitoring depending on the size, location and clinical presentation. Reversing clotting problems (mostly related to blood thinner use) immediately is important to limit worsening or recollection of the subdural bleed.

SDH can be related to major or minor head trauma. It might also be seen in the absence of any perceived head trauma, this form mostly occur in older adults with brain atrophy. This type called chronic ("spontaneous") SDH is becoming more frequent with aging of the population, current estimates suggest about 38000 chronic SDHs per year in the US alone. Use of blood thinners and particularly anticoagulants is a known risk factor for both trauma related and chronic SDHs. Even lower intensity blood thinners such as aspirin can also increase the risk. Alcohol use is also a risk factor for both types through increasing the fall risk and alcohol's action on platelets increasing bleeding risk.

Avoiding falls and being cautious about blood thinner use in patients at risk are important approaches to prevent SDH. There is no other imaging marker of high risk but having sustained a SDH is shown to increase risk of subsequent SDHs.