Summary Dangerous and severe personality disorder (DSPD) services have a relatively short history, are currently under review and may be reconfigured in the next few years. Despite such uncertainties, implementation of therapeutic programmes for patients and prisoners in this category is likely to remain a high priority. We describe the background to the DSPD initiative in England and consider issues that arose 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 further challenges in delivering treatment and suggest that ongoing evaluation of treatments is critical in this area of practice, given the impoverished knowledge base.