Dissecting aneurysms occur when blood extrudes into the wall of a vessel. Posterior circulation dissections are recognised as an important cause of cerbral infarction and subarachnoid haemorrhage(SAH), however posterior inferior cerebellar artery (PICA) aneurysmal dissections are rare. A 49-year-old man who presented with SAH was found to have a left PICA dissection on cerebral angiography. The lesion was treated with surgical clipping proximal to the dissection and a distal PICA to PICA anastomosis. The pathology, diagnosis, presentation and treatment of these difficult lesions is discussed.