A high proportion of people who receive care in medium secure forensic psychiatry services have co-morbid drug and/or alcohol problems. Substance misuse is an important issue in the management of patients and may also be implicated in relapse, re-offending, and re-admission after discharge. Little is known about the capability of staff to manage patients' co-morbid substance misuse. Survey questionnaires, developed following depth interviews and a focus group, were sent to managers of the 28 National Health Service-managed medium secure units in England and to the 145 consultant forensic psychiatrists with admitting rights to these units. Returns were received from 27 unit managers (96%) and 101 consultants (adjusted response rate of 75%). Substance misuse had occurred in all units in the previous year. Despite this, relatively few unit staff had specialist substance misuse training; just 16 (59%) units had substance misuse treatment programmes for in-patients and staff played little role in the management of substance misuse after patients were discharged. There was uncertainty about the best model of care for substance misuse and links with specialist substance misuse services were poorly developed. It is likely that many patients are inadequately treated for their co-morbid substance misuse problems in English medium secure units and after discharge.