Between the late 19th and the mid-20th centuries, puberty science enormously expanded the field and the reach of its intervention: from the management of the few to the surveillance of all. The assumption of morbidity as endemic to sexual maturation is rooted in the idea that puberty entails a ‘crisis’ for the child. This notion keeps reappearing, albeit in altered forms, in representations of adolescence and wherever there is talk about sexually developing children. Puberty is popularly deemed a profound and almost sudden transformation of body and behaviour – a ‘revolution’, to use a recurrent metaphor of 19th-century physiologists. In Hippocratic or Galenian medicine ‘crisis’ is the moment at which any given condition is expected to either regress or transition into a chronic or deadly state. In Hippocratic medicine, just as there were diseases that reached a crisis on ‘critical days’, there were also diseases that reached their ‘critical’ time at about the coming of age.