We outline the development of a Mental Health Domain to track accessibility and quality of mental health care in the United States Veterans Health Administration (VHA) as part of a broad-based performance measurement system. This domain adds an important element to national performance improvement efforts by targeting regional and facility leadership and providing them a concise yet comprehensive measure to identify facilities facing challenges in their mental health programs. We present the conceptual framework and rationale behind measure selection and development. The Mental Health Domain covers three important aspects of mental health treatment: Population Coverage, Continuity of Care, and Experience of Care. Each component is a composite of existing and newly adapted measures with moderate to high internal consistency; components are statistically independent or moderately related. Development and dissemination of the Mental Health Domain involved a variety of approaches and benefited from close collaboration between local, regional, and national leadership and from coordination with existing quality-improvement initiatives. During the first year of use, facilities varied in the direction and extent of change. These patterns of change were generally consistent with qualitative information, providing support for the validity of the domain and its component measures. Measure maintenance remains an iterative process as the VHA mental health system and potential data resources continue to evolve. Lessons learned may be helpful to the broader mental health-provider community as mental health care consolidates and becomes increasingly integrated within healthcare systems.