The Diagnostic and Statistical Manual of Mental Disorders—Fifth Edition (DSM-5) diagnostic criteria for intellectual disability (ID) include a change to the definition of adaptive impairment. New criteria require impairment in one adaptive domain rather than two or more skill areas. The authors examined the diagnostic implications of using a popular adaptive skill inventory, the Adaptive Behavior Assessment System–Second Edition, with 884 clinically referred children (ages 6–16). One hundred sixty-six children met DSM-IV-TR criteria for ID; significantly fewer (n = 151, p = .001) met ID criteria under DSM-5 (9% decrease). Implementation of DSM-5 criteria for ID may substantively change the rate of ID diagnosis. These findings highlight the need for a combination of psychometric assessment and clinical judgment when implementing the adaptive deficits component of the DSM-5 criteria for ID diagnosis.