PURPOSE: This study explored the health care transition (HCT) experiences of parents of adolescents and young adults (AYAs) with intellectual disability (ID), 18-33 years of age, including barriers and facilitators to the AYA's transition to adulthood within and between the medical, educational, community, and vocational systems. DESIGN AND METHODS: A qualitative descriptive design with semi-structured individual interviews with 16 parent participants was used. Purposive sampling of parents was utilized with variation on race/ethnicity and AYA age, stage in transition, and condition. This study was conducted through a major medical center in the southeast United States. Content analysis was utilized. RESULTS: Three overarching themes represented the factors and essence of supporting AYAs with ID transition to adulthood. Inefficient and siloed systems illuminated barriers families are commonly experiencing within and between the medical, educational, community, and vocational systems. 'Left out here floundering' in adulthood, described the continued inadequacy of resources within each of these systems and parent's having to find available resources themselves. Hope despite uncertainty, included the perceived costs and benefits of their AYA's disability and the value of parent peer support in providing key knowledge of resources, strategies, and perspectives. CONCLUSIONS: Our findings illuminate the need for improved infrastructure to provide effective HCT and partnerships to help integrate HCT support within other life course systems. Results support the rationale for non-categorical HCT-focused approach. PRACTICE IMPLICATIONS: A parent peer coach-facilitated intervention offers promise for bridging the gap between systems and meeting family needs.