Patients with a chronic subdural hematoma (cSDH), that is, a blood accumulation between two meninges developing over a long period of time, often have recurrent bleedings after an initial operation. The study aims to show that additional surgery reduces the risk of recurrent bleeding. The additional procedure aims to block small blood vessels in the skull with tiny plastic particles. The small blood vessels are embolized using X-rays and a contrast medium and a fine tube that is inserted into the diseased vessels of the head via the groin. Patients of full age who have undergone burr hole trepanation as a first operation, i.e. a blood drain through a hole in the cranial cavity, can participate in the study. Participating patients are randomly assigned to a control group with treatment according to clinical routine or a treatment group with an additional occlusion of the blood vessels in the skull. In addition, patients can consent to a genetic test to determine the relationship between a coagulation factor and the risk of recurrence of the hematoma. In order to record the test results, check-up examinations are carried out after one and three months.