Since 1991, the Minimum Data Set 2.0 (MDS 2.0) has been the mandated assessment in US nursing homes. The Resource Utilization Groups III (RUG-III) case-mix system provides person-specific means of allocating resources based on the variable costs of caring for persons with different needs. Retrospective analyses of data collected on a sample of 9707 nursing home residents (2.4% had an intellectual disability) were used to examine the fit of the RUG-III case-mix system for determining the cost of supporting persons with intellectual disability (intellectual disability). The RUG-III system explained 33.3% of the variance in age-weighted nursing time among persons with intellectual disability compared to 29.6% among other residents, making it a good fit among persons with intellectual disability in nursing homes. The RUG-III may also serve as the basis for the development of a classification system that describes the resource intensity of persons with intellectual disability in other settings that provide similar types of support.