Heparin-induced thrombocytopenia (HIT) is an antibody-mediated drug reaction to heparin use that causes platelet aggregation, followed by thrombocytopenia. Despite the thrombocytopenia, the main complications of HIT are thromboembolic in nature rather than hemorrhagic, and in particular, intracranial hemorrhage is rare. Herein, we describe a case of atraumatic acute subdural hematoma secondary to HIT, which was treated by platelet transfusion and surgery. A 77-year-old woman was admitted to our hospital for the treatment of severe aortic valve stenosis. Unfractionated heparin was administered during the preoperative period and during the aortic valve replacement surgery. Three days after the cardiac surgery, the patient presented with coma consistent with an acute subdural hematoma in the posterior fossa and obstructive hydrocephalus. Laboratory examination revealed a marked decrease of the platelet count to 40000/µL, and subsequent serological assay confirmed the diagnosis of HIT. The patient was treated by transfusion of platelets and fresh frozen plasma, and surgical removal of the hematoma. We started the administration of argatroban for substitution of heparin 4 days after the craniotomy. On day 13 after the neurosurgery, the patient developed cerebral infarction due to left middle cerebral artery occlusion and persistent right hemiparesis. We presented a rare case of the patient who developed acute subdural hematoma complicating HIT. Emergency craniotomy was successfully performed after administering platelet transfusions. Our experience with the present case suggests that platelet transfusions may be effective for performing emergency surgery for intracranial hemorrhage, even in patients with HIT.