The posterior inferior cerebellar artery has a curved course in the region of the medulla oblongata. Besides its frequent individual variations, this vessel exhibits three morphological types: in type 1 (the commonest type, i.e. more than 50% of the cases) it curves with its vertex turned upwards; in type 2, the posterior inferior cerebellar artery turns in a gentle arch on to the posterior surface of the medulla oblongata, so there is no real curve; in type 3, the posterior inferior cerebellar artery curves but its vertex turns downwards. In all of these cases, the artery is in close relationship with the last four cranial nerves. This relationship is most characteristic in the 1st and 3rd types. The morphological types could be recognised on the angiograms.