The authors report clinical, eletro-encephalographic and anatomo-pathological findings in two patients with akinetic mutism. One case showed a tumor (rabdomiosarcoma) in the left hemisphere of the cerebellum, with bulbar compression; in the other case, a neurinoma was found in the left cerebellopontine angle, with atrophy by compression of the surrounding tissue. Psycopathologically, akinetic mutism was related to the concept of akinesia, as understood by Kleist, i. e., changes in the motoric excitability connected with pathological variation of the instinctive stimuli for global movement. The instinctive drive of the impulse was integrated with the nutrition instinct and subordinated more directly to the sexual instinct, according to organological concepts which transfer the site of these functions from the hypothalamic region to the cerebellum. The authors suggest, thus, that akinetic mutism may be the result of rupture of the encephalou's functional harmony, through activation of an innibitory mechanism in the cortical systems. According to this concept, and based on modern neurophysiological research on the cerebellum, the authors admit that the lesions found in the cerebellum in the two cases reported, may be considered as responsible for akinetic mutism, through supressive mechanisms located in the reticular system. They suggest, therefore, that the cerebellum may be included in the structural system, the changes of which are responsible for akinetic mutism, which other authors have already integrated in the mesencephalo-diencephalic region (Cairns, Bailey, French e Magoun) and, at cortical levels, in the anterior part of the cingulate gyri (Nielsen and als., Barris and Schumann).