We examined the subjective health and well-being of 389 transition-age youth with autism or intellectual disability using the parent proxy version of the KIDSCREEN-27. Parents reported well-being of youth with autism and youth with intellectual disability lower than a normative sample in the domains of Physical Well-being, Psychological Well-being, and Social Support and Peers. For both groups of young people, the lowest ratings were reported in Social Support and Peers. Higher ratings of well-being in one or more domains were predicted by minority status, youth character strengths, involvement in community activities, and religious faith. Challenging behaviors, autism, age, and speech as the primary mode of communication were predictive of lower ratings of well-being. We discuss implications for special educators and service providers and offer directions for future research.