The first paper of this sequence discussed the division of childhood psychoses into those with onset before the age of 3 (infantile psychoses, I.P.) and those with onset after the age of 5 (late onset psychoses, L.O.P.). The second paper described in detail the clinical phenomena in 80 psychotic children so classified at Oxford or Newcastle (see Table I), and showed that this division corresponded to clear-cut distinctions in the clinical pictures. The I.P. group showed gaze avoidance, abnormal pre-occupations, self-isolating patterns of behaviour, echolalia, overactivity. The L.O.P. group showed hallucinations and thought disorder. With these two groups clearly established we now look to see whether anything in their family and background also distinguishes them.