1. Cases are reported in which a definite change in personality appeared at puberty, with the actual psychosis developing later.2. Most of the cases also gave a history of rapid growth or other disturbance or metabolism at puberty.3. The relation of puberty to psychopathic behavior is discussed.4. In certain cases of dementia præcox it is difficult to determine whether seclusive behavior appearing at puberty is a part of the personality or a part of the psychosis.