To promote health care transition services (HCTS) among youth with autism spectrum disorder (ASD), it is important to understand their access to HCTS and the association with functioning. We conducted weighted descriptive statistics and regressions. Findings suggested that HCTS were inconsistently provided to youth with ASD. Access to two or more HCTS was associated with positive social-emotional functioning. Helping youth with ASD understand health care changes and working with them to gain skills in managing health needs were found to be significant determinants of positive social-emotional functioning. The present study sheds light on HCTS that are essential for youth with ASD and highlights the necessity of health care system changes to promote service access and optimal functioning for youth with ASD.