Previous research seems to indicate that a substantial percentage of patients with delayed sleep phase syndrome (DSPS) also suffer from personality disorders. In the present study, we attempted to ascertain whether, in a population of hospitalized psychiatric patients, we would find a greater frequency of DSPS among patients suffering from personality disorders than among patients suffering from any of the other psychiatric disorders. Sixty-three hospitalized adolescents took part in the study. None of them had any diagnosed medical disorders, and all were being treated with psychiatric drugs. Ten subjects were diagnosed as suffering from DSPS according to a sleep-wake schedule structured interview. As hypothesized, subjects diagnosed as suffering from personality disorders had a significantly higher probability of also suffering from DSPS. Additional findings were that patients with DSPS were more likely to have received an Axis II diagnosis only, and were more likely to be diagnosed as suffering from a distinct group of disorders characterized by affective lability. The latter finding may be due to the sleepiness that accompanies DSPS. The findings of the present study suggest that there may be an interrelationship between DSPS and personality disorders, and may lend some support to the hypothesis that inborn peculiarities in the sleep-wake rhythm lead to the social and functional difficulties characteristic of personality disorders.