A 37-year-old man presented with perimesencephalic non-aneurysmal subarachnoid hemorrhage associated with cavernous sinus thrombosis. Anticoagulant therapy was administered to treat the cavernous sinus thrombosis, but provoked severe intracranial hemorrhage, severely disabling the patient. Perimesencephalic non-aneurysmal subarachnoid hemorrhage is a benign clinical entity with generally good prognosis, but the association with cavernous sinus thrombosis requires careful investigation prior to treatment.