A 76-year-old man presented with brain stem hemorrhage after burr-hole drainage for bilateral chronic subdural hematomas. Neuroimaging demonstrated resolution of the transtentorial herniation but also detected new brain stem hemorrhage, manifesting as gait disturbance. He recovered after conservative treatment. Asymmetrical and rapid decompression, which leads to vascular disruption and/or sudden increase in cerebral blood flow, was probably responsible for the secondary brain stem hemorrhage. Therefore, simultaneous and bilateral decompression with a slow rate of evacuation of massive bilateral chronic subdural hematomas is recommended to prevent serious complications such as secondary intracranial hematoma.