This article analyzes the reliability and factor structure of the Self-Determination Inventory: Adult Report (SDI:AR) in adults with and without intellectual disability. There is a critical need for contemporary assessment tools given the emphasis on self-determination outcomes in disability supports and services. The findings suggest that the same set of items can be used across adults with and without intellectual disability. However, there are significant differences in overall self-determination across adults with and without intellectual disability, with adults with intellectual disability scoring lower on the SDI:AR. Implications for research and practice are discussed.