The incidence of chronic subdural hematomas from 1990 to 2015 in a defined Finnish population. 
OBJECTIVE: The aim of this study was to determine the population-based epidemiology of chronic subdural hematoma (CSDH) over a 26-year period.  METHODS: A retrospective study was conducted of all adult patients (≥ 18 years and residents of Pirkanmaa [Finland]) with a diagnosis of CSDH between 1990 and 2015.  The cases were identified using ICD codes.  Detailed data collection was performed using medical records and death certificates.  All patients were monitored until death or the end of year 2017.  The annual number of inhabitants in the Pirkanmaa region was obtained from Statistics Finland (Helsinki, Finland).  RESULTS: A total of 1168 patients with CSDH were identified from hospital records and death certificates; patients were considered as new-incidence cases if 2 years had elapsed following primary treatment and in cases involving a new contralateral CSDH.  From 1990 to 2015, the overall incidence of CSDH doubled from 8.2 to 17.6/100,000/year.  Among adults younger than 70 years, the incidence remained quite stable, whereas the incidence clearly increased among the ≥ 80-year-old population, from 46.9 to 129.5/100,000/year.  The median age for a CSDH diagnosis increased from 73 to 79 years during the 26-year period.  Head trauma was documented in 59% of cases.  A ground-level fall was related to the CSDH in 31% of patients younger than 60 years and in 54% of those 80 years or older.  The proportion of alcohol-related cases decreased toward the end of the study period (1990-1995: 16% and 2011-2015: 7%), because alcohol abuse was less frequent among the growing group of elderly patients.  In contrast, the percentage of patients receiving anticoagulant or antiplatelet medication almost doubled toward 2015 (1990-1995, 27%; and 2011-2015, 49%).  The patients' neurological condition on admission, based on both Glasgow Coma Scale score (score < 13: 1990-1995, 18%; and 2011-2015, 7%; p < 0.001) and the modified Rankin Scale score (score 0-2: 1990-1995, 8%; and 2011-2015, 19%; p < 0.001), was better in recent years than in the early 1990s.  CONCLUSIONS: From 1990 to 2015, the incidence of CSDH has increased markedly.  The incidence of CSDH among the population 80 years or older has nearly tripled since 1990.  The use of anticoagulants has increased, but there has been no change regarding the ratio between a traumatic and a spontaneous CSDH etiology.  As the world population becomes progressively older, the increasing incidence of CSDH will be a burden to patients and a future challenge for neurosurgical clinics.