Seven of one hundred twenty-one patients with chronic myeloid leukemia (CML) treated with imatinib mesylate developed subdural hematomas. All had advanced disease and were treated initially at a dose of 600 mg per day. Three patients had thrombocytopenia (platelet < 10 x 10(9)/l), one had leukocytosis (white blood cell count > 150 x 10(9)/l) and three had neither around the time of diagnosis of the subdural hematomas. Four patients required surgical evacuation. One patient, in blast crisis, died as a consequence of the subdural hematoma. Three patients survived but died of progressive CML. The remaining three patients having recommenced imatinib, are alive and well, and one has achieved a major cytogenetic response. Subdural hematomas must be considered even in mildly symptomatic patients receiving imatinib regardless of their peripheral blood counts. Patients who survive can be cautiously restarted on imatinib. Further studies are required to study the potential relationship between imatinib mesylate and subdural hematomas.