Using principles of community-based participatory research we developed a new theory-based measure of health-related quality of life (HRQOL) for individuals with intellectual disability (ID). We recruited adults with ID (n = 129) to take part in interviews and review successive versions of HRQOL items. Critical input about content and understandability shaped the items, as did input from four focus groups of parents/caregivers (n = 16) and representative stakeholders from community-based agencies (n = 7). The resulting HRQOL measure, called the HRQOL-IDD, contains 42 items. The response format depicts a gradient of fluid-filled cups (“none” to “full”) to represent frequency of experience of each item on a 5-point scale.