BACKGROUND : A number of randomized controlled trials have shown the benefit of drain placement in the operative treatment of chronic subdural hematoma (CSDH); however, few reports have described real-life results after adoption of drain placement into clinical practice. We report the results following a change in practice at Helsinki University Hospital from no drain to subdural drain (SD) placement after burr hole craniostomy for CSDH. METHODS : We conducted a retrospective observational study of consecutive patients undergoing burr hole craniostomy for CSDH. We compared outcomes between a 6-month period when SD placement was arbitrary (July-December 2015) and a period when SD placement for 48 hours was routine (July-December 2017). Our primary outcome of interest was recurrence of CSDH necessitating reoperation within 6 months. Patient outcomes, infections, and other complications were assessed as well. RESULTS : A total of 161 patients were included, comprising 71 (44%) in the drain group and 90 (56%) in the non-drain group. There were no significant differences in age, comorbidities, history of trauma, or use of antithrombotic agents between the 2 groups (P > 0.05 for all). Recurrence within 6 months occurred in 18% of patients in the non-drain group, compared with 6% in the drain group (odds ratio, 0.28; 95% confidence interval, 0.09-0.87; P = 0.028). There were no differences in neurologic outcomes (P = 0.72), mortality (P = 0.55), infection rate (P = 0.96), or other complications (P = 0.20). CONCLUSIONS : The change in practice from no drain to use of an SD after burr hole craniostomy for CSDH effectively reduced the 6-month recurrence rate with no effect on patient outcomes, infections, or other complications.