Researchers and Institutional Review Board (IRB) members' attitudes influence scientific knowledge about individuals with intellectual disability. We recruited 260 intellectual disability researchers and IRB members to develop a measure of attitudes toward the research participation of adults with intellectual disability, the Participation in Research Attitude Scale. Findings suggest three conceptual domains: Opportunity and Choice, Help in Decision Making, and Beneficence. We also examined individual differences in attitudes and the relationships between general and specific attitudes. In general, intellectual disability researchers and those with closer relationships to individuals with disabilities had attitudes consistent with disability-rights principles. Some dimensions of global attitudes toward adults with intellectual disability predicted more specific attitudes toward their research participation. Implications are discussed.