Background: There remains a severe lack of evidence on the effectiveness of community services for adults with psychosis and intellectual disabilities (ID). There has been little consensus even of what services should provide for this service user group. Method: A consultation of multidisciplinary professionals was carried out by using a three-round Delphi exercise. Participants were recruited nationally. They rated their views on the importance of 139 items for the care of adults with psychosis and ID. These included 85 routine service components, 23 service user characteristics for those needing a more intensive service and 31 more intensive service components. Results: Forty-nine out of 52 participants completed all three rounds of the Delphi consultation. Consensus of opinion (greater than or equal to 80% agreement as essential) was obtained on 18 of the routine service components, nine of the service user characteristics and five of the more intensive service components. The routine service components considered essential can be broadly considered under a need for a focused approach on the service user and their illness (e.g. monitoring of mental state) and the added need to work within the wider context of the service user with psychosis and ID (e.g. access to social, leisure or occupational activities). Five of the more intensive service components were considered to be essential (e.g. can react to a crisis that day). However, the routine service components considered essential already contained many components such as out-of-hours support and crisis plans also relevant to more intensive services. Conclusion: These findings can be used to develop further the evidence base for services in the community for this user group and to assist in the preparation of much needed service evaluation studies.