Introduction: Despite the high prevalence of mental health issues for young people with intellectual disability (ID), young people with ID can struggle to receive the mental health support they need. The aim of this study was to examine a new community-based, clinical mental health service for young people (12-25 years) with co-occurring ID and mental illness, and to explore the outcomes for young people and experiences of families who received service from the new program. Methods: Two studies were conducted using qualitative and quantitative research methods. First, using the Health of the Nations Outcome Scales (HoNOS), a quantitative longitudinal study was conducted to measure any changes in young people's behavioral and social issues, mental health, and levels of impairment, from the being accepted to the service till the completion of care (n = 23). A second study involved qualitative interviews with parents/carers who attended the service (n = 10) that were analyzed to look for emerging themes in parents'/carers' experience of the service. Results: Results of study 1 indicated that young people's behavioral issues and social problems decreased from the time of admission to their completion of carer. Further, results of Study 2 revealed that parents/carers considered the mental health and behavior of their child had improved from being in the program. Parents also valued the person-centered, multidisciplinary, co-ordinated approach of the service, and viewed the new program as an improvement on previous services they had experienced. Conclusions: This study provides preliminary support for the efficacy of the new program and suggests future specialist dual disability services may look to a family-focused, multidisciplinary approach that includes assessment, treatment, and management as an effective treatment model.