Dangerous and severe personality disorder (DSPD) services have a relatively short history but are increasingly involved in the implementation of therapeutic programmes. We describe the background to the DSPD initiative in England and consider issues that arise in planning and delivering treatment services. Two bodies of evidence are particularly relevant: previous research into personality disorder and its treatment, which we suggest is as yet of limited value, and research into the outcomes of offender treatment programmes. The latter is clearly relevant but greater consideration of adapting programmes for the patient population and of breadth of treatment is required in the DSPD setting. The important task is to integrate components for the treatment of personality disorder and offending behaviour in a holistic manner. We describe three further challenges in delivering treatment and suggest that ongoing evaluation of treatments is critical in this area of practice, given the impoverished knowledge base.