The author describes his Form E-2 checklist method for the diagnosis of early infantile autism and differentiation of other childhood psychoses. Data on 2,218 psychotic children, 1,652 boys and 556 girls, are presented. The checklists showed 9.7% of the children to have early infantile autism, thus providing a confirmation of Kanner's 1962 estimate that only 10% of his patients called autistic by others were correctly diagnosed. Also presented are data showing that among 445 psychotic children seen by two different diagnosticians, only 55 had been assigned the same diagnosis twice. Laboratory studies and other sources are cited to show that Form E-2 is effective in differentiating truly autistic from autistic-type children. Other aspects of the problem of diagnosing psychotic children are discussed.