A 65-year-old female presented with an extremely rare case of a ruptured thrombosed large aneurysm of the anterior inferior cerebellar artery (AICA) in which a local hematoma compressed the medulla oblongata and caused acute respiratory failure. She first presented with dizziness, general fatigue, and nausea 2 months before admission. She was hospitalized for intense general fatigue, nausea, and occipitalgia. Computed tomography and T(1)-weighted magnetic resonance imaging showed a heterogeneous lesion around the right cerebello-medullary cistern. Angiography revealed a fusiform aneurysm of the right AICA. Asphyxia occurred 4 days after admission and the patient underwent an emergency operation. No subarachnoid hematoma was present, but a hematoma around the ruptured portion markedly compressed the medulla oblongata. The medulla oblongata was adequately decompressed after subtotal removal of the aneurysm. The patient's respiratory status and consciousness level recovered after the operation.