The presence of co-occurring psychiatric disorders among individuals with developmental disability (DD) requires clinicians to adjust and modify standard mental health assessment and treatment planning. In particular, assessment includes input from a multi-disciplinary team and as a result, diagnosis is frequently a synthesis of data from many different points of view. Treatment planning and implementation commonly include a collection of highly specialized, individualized programs that focus on the long term management of both disorders. Crises and recurrence of mental disorders are commonplace in part due to the presence of ongoing risk and vulnerability factors for mental disorders. As a result, the need for emergency interventions, specialized respite services, hospitalization and other transition services is extensive. The quality, availability and access to these services vary considerably. Many programs are concentrated in metropolitan or university-based centers and pose hardships based on geographic distance. The availability and utilization of services is affected by political, economic, socio-cultural and psychological forces that impact both the willingness to use services and the distribution of professionals trained and qualified to manage individuals with dual diagnoses. The complex interaction between each of these factors determines the structure, function, and capacity for innovation built into current service models.