Using recently published general population studies, this chapter updates an earlier Moran review on the epidemiology of ASPD. It examines the prevalence, comorbidity, psychosocial functioning, impact on health services and cultural differences of those with ASPD and, to a lesser extent, of those with psychopathy and on prisoners. It finds that the prevalence of ASPD ranges between 0.6% and 4.3% in men (which is significantly higher than in women). It has multiple comorbidities – both with other mental disorders (especially with substance misuse and affective disorder) together with other Cluster B PDs. Despite significant mental health and psychosocial impairment, those with ASPD rarely seek treatment for their disorder. There are marked cultural differences in the prevalence of ASPD with studies in the United States showing significantly higher rates than in Europe or in Asia. The prevalence of ASPD among prisoners is c. 55% among men and 31% among women with community prevalence rates for psychopathy ranging from 0.6% in the United Kingdom and 1.0% in the United States. Both ASPD and psychopathy have a positive association with both increased mortality and suicidality, suggesting that, together with their other impairments, they are a group that require mental health interventions.