Chronic subdural hematoma (CSDH) is a common disease. The main treatment is neurosurgical evacuation and subsequent hematoma drainage. However, consensus on the optimal drain placement site, and whether the drainage should be active or passive, is lacking. The aim of the current study is to test the hypothesis that 24 hours active subperiosteal drainage is non-inferior to 24 hours passive subdural drainage after single burr hole evacuation of a unilateral CSDH. The study is a multicenter randomized non-inferiority trial encompassing all neurosurgical units in Denmark. Adult patients with symptomatic CSDH admitted to a Danish neurosurgical unit for single burr hole evacuation will be screened for inclusion. Patients who are not able to give informed consent, and patients with recurrent CSDH, known cerebrospinal fluid abnormalities, and other known brain pathologies will be excluded. Patients with bilateral CSDH will be registered as one case and treated similarly on both sides. Before surgical hematoma evacuation patients will be randomized to 24-hour passive subdural drainage or 24-hour active subperiosteal drainage. The patients included and the two study statisticians will be blinded. The primary outcome is a composite outcome of 90-day mortality and symptomatic CSDH recurrence. Secondary outcomes are 90-day simplified modified Rankin score (smRSq), and complications related to surgery or occurring during admission, including intracerebral hemorrhage due to misplaced drains, acute subdural hematoma, tension pneumocephalus, wound infection, drain seepage, subperiosteal hematoma, thromboembolic events, infections and seizures. Sample size simulations of non-inferiority with a threshold of 7% increased relative risk show that a total of 354 participants will be required to demonstrate a relative risk reduction of recurrent CSDH and mortality of 30% for the cohort receiving active subperiosteal drainage given a stable power above 80% with an alpha of 5%. The study inclusion period is estimated to last 2 years. Ethics approval for inclusion of competent patients has been obtained (N-20240009).