Intelligence tests and adaptive behavior scales measure vital aspects of human functioning. Assessment of each is a required component in the diagnosis or identification of intellectual disability. The present study investigated the population correlation between intelligence and adaptive behavior using psychometric meta-analysis. The main analysis included 148 samples with 16,468 participants. Following correction for sampling error, measurement error, and range departure, analysis resulted in a population correlation of ? = .51. The most pertinent moderator analysis indicated that the relation between intelligence and adaptive behavior tended to decrease as IQ increased. The theoretical prevalence of intellectual disability is affected not only by IQ and adaptive behavior cut scores but also by the correlation between the two; thus, these findings inform practice and policy related to eligibility criteria and prevalence of intellectual disability.