A 43-year-old woman complaining of severe pain of the right side of the face was admitted to the Department of Neurosurgery. It had been present for three months and diagnosed as trigeminal neuralgia. The CT scan without contrast material had been considered normal at that time. Three months later, after a favourable response to carbamazepine, she suddenly developed right occipital headache and drowsiness. On admission, she was alert, and neurological examination revealed only mild neck stiffness. Computed tomographic scan demonstrated an acute hematoma in the right cerebellopontine angle and in the fourth ventricle. Vertebral angiography revealed an aneurysm of the right anterior inferior cerebellar artery (AICA). A posterior fossa approach disclosed a large, nearly totally thrombosed, saccular AICA aneurysm, which showed minimal compression to the pens at the trigeminal root entry zone. The aneurysm was clipped and excised. She showed an excellent recovery and was free of pain in the early postoperative period and at the last examination 16 months later. Aneurysms in the distal AICA are very rare lesions. Only 31 cases have been published so far. Distal AICA aneurysm in an extremely unusual cause of trigeminal neuralgia secondary to aneurysmal compression. The literature concerning AICA aneurysms and their clinical manifestations is reviewed and discussed.