1. Three major groups of psychoses in child hood can be distinguished by their age of onset: under 3 years, 3-5 years and over 5 years.
2. Diagnostic criteria are proposed for the first and third groups, based on the work of Kanner and Creak for the first, and Fish (in adult schizophrenia) for the third.
3. The study reported in the following papers tests the value of distinction by age of onset and establishes the frequency of occurrence of the different signs in the different clinical groups, leading to discriminants for differential diagnosis.