Service systems in health and community agencies are struggling to deliver mental health services to adults with an intellectual disability. Many professionals feel ill equipped to assess and treat mental health disorders in this population. This Australian case study describes the collaborative effort required to meet the complex health needs of a client with an intellectual disability and the needs of her family, and the role played by a specialist, Disability Health Service. The key elements of this successful interagency collaboration are outlined and include good communication, adequate resourcing, and a willingness to resolve dynamic tensions and learn from each other.