XYY males. Some clinical and psychiatric aspects deriving from a survey of 1,811 males in hospitals for the mentally handicapped.

A survey of 1,811 mentally handicapped males in eighteen hospitals is described. Males discovered with supernumerary Y chromosomes numbered 15, of whom 12 were 47,XYY. Some of the physical, social, psychological and psychiatric findings are described and compared with groups matched for IQ and height. The main psychiatric findings are diminished intelligence, retardation in development of secondary sexual characteristics, and poor emotional control leading to inadequate social adaptive patters which are described and discussed.