A pathological study has been carried out of 49 examples of medullary infarction in 33 patients. The medial infarcts, very seldom single ( 2 12), spared the subolivary levels. The pontomedullary junction was affected in 3 9 cases studied. The lesions were more frequent in the ventral part of the arterial zonal pattern. They more often extended to its dorsal part at the level of the middle and upper one-third of the olive. The lateral infarcts, seldom single ( 6 30), extended to the subolivary levels in 6 22 cases studied and to the pontomedullary junction in 9 24 cases. The structures involved in each case and the area of the lesions at each cranio-caudal level have been studied. None of the 7 dorsal infarcts was single; in 6 of these cases there was also a cerebellar infarct involving the area of supply of the posterior inferior cerebellar artery. The subolivary levels ( 1 6) and ponto-medullary junctions ( 1 6) were seldom affected. The extent of the lesions in these uncommon infarcts has been described in detail. © 1976.