Stammering is a neurosis of child speech arising in the period of violent quantitative and qualitative changes in the development of speech. Its origin is determined by the convergency of disposition and trauma. By »disposition« we mean the immaturity of the child’s brain in general as well as the period in which physiological difficulties are encountered in speech development; more especially then the excitation weakness of the speech analyser, conditioned by organic changes (both diffused and localised, inborn and acquired) as well as by functional changes (crossed dominance, the state of non-dominance). Thus the »disposition« is the sum of biological factors. The evoking momentum of stammering is the trauma of speech , function: here it is a question of social factors with an acute or chronic effect. The greater the trauma, the less disposition is sufficient to give rise to stammering. The traumatisation of the speech function brings about its neurotisation: regression to lower link stages, fixation of the symptoms on the individually experienced life situations, potentiating and increasing the number of symptoms by transfer to similar situations. Attached is an attempt at a pathological explanation of the origin and symptomatology proceeding from the fact that the basis of paroxysm is the pathological increase in excitation and inhibition. The pathogenesis being thus known, natural directives for prevention result from it. This is done in families by spreading pedagogical knowledge; the best prevention in nursery schools is the established and successful system of education of speech.