BACKGROUND Chronic subdural hematoma is defined as collection in the subdural space for more than 3 weeks. The incidence ranges from 1 to 20 per 100 000/year, with increased prevalence in the elderly, in males, and with use of anticoagulants or antiplatelets. Chronic myeloid leukemia has been linked to spontaneous subdural hematoma, with the highest reported cases of 39 patients in Korea, but no management is mentioned in that paper. There are few reported cases of patients who are medically free with no use of anticoagulants, diagnosed as having a subdural hematoma and then later discovered to have chronic myelogenous leukemia. CASE REPORT We report the case of a 45-year-old man, with known hypertension and diabetes mellitus type 2, on aspirin weekly, who was referred from another hospital with a history of sudden-onset severe headache not related to trauma. Computed tomography (CT) of the brain done in the other hospital showed a left-side subdural hematoma with midline shift. He underwent left-sided acute subdural hematoma evacuation and decompressive hemicraniectomy. He was started on hydroxyurea for chronic myelogenous leukemia. CONCLUSIONS A lesson from this rare case is to look for a differential diagnosis and to keep chronic myelogenous leukemia in mind in patients with leukocytosis. Also, we recommend sending a hematology referral in nontraumatic subdural hematoma. There is no specific treatment or algorithm based on previous research, although from observed data and based on information from the American Heart Association, it is reasonable to perform craniectomy in extra-axial collections of more than 1 cm with midline shift to avoid mortality, as reaching a diagnosis would take too much time.