Four cases are presented, with bulbo-spinal muscular atrophy characterised by adult onset and rapid evolution. They belong to a family in which the type of inheritance is probably dominant. Two cases were studied histologically. The most striking feature was the disappearance of neurons in the lower motor nuclei of medulla and of the spinal anterior horns. An electron microscopic study was carried out in one case. Accumulation of neurofilaments was a general characteristic, in addition to the picture of different sized spheroids. The clinical-pathological relationship is discussed.