One of the most important questions in dealing with psychopaths is the prognosis. In 1948 two of us made a study (Stafford-Clark, Pond, Lovett-Doust, 1951) of a number of criminal psychopaths and a control group of ordinary criminals in prison by clinical and EEG methods, with the object of revealing the characteristics which most significantly distinguished psychopaths from others, and which were, therefore, most crucial in diagnosis. The psychopaths were carefully chosen in collaboration with two experienced prison medical officers. The later criminal behaviour of these psychopaths and controls is equally interesting, however, if we are to understand what the diagnosis implies (Gibbens, 1951). The third author (T.C.N.G.) has therefore been conducting a continuous follow-up, with the collaboration of the Prison Commission and Criminal Records Office. The results of the first follow-up, from 1948–1953, have been published (Gibbens, Pond and Stafford-Clark, 1955), and were reproduced in the transactions of the Royal Commission on the Law relating to Mental Illness (1957). The present paper deals with a further period of study, so that the follow-up is now from 1948-June, 1957.