The aim of the present study was to characterize the subjective and objective sleep and sleep quality in habitually violent offenders with DSM-IV diagnosis of antisocial personality disorder using a sleep questionnaire, actigraphy, polysomnography and power spectral analysis. Subjects for the study were 19 drug-free males (mean age ± SEM 30.7 ± 2.58 years) recruited from a forensic psychiatric examination in a special ward of a university psychiatric hospital. The most striking finding was the high amount of slow-wave sleep, particularly the deepest S4 stage (17% as compared with 6% in healthy controls), in males with antisocial personality disorder. Moreover, in the spectral power analysis, both the delta and the theta power were significantly elevated. Whether this increase in persons with antisocial personality disorder reflects a specific brain pathology, or a delay in the normal development of sleep patterns in the course of ageing needs to be clarified with further experiments.