Knowledge is needed about specific supports and barriers for successful transitions to adulthood for autistic youth, especially from the perspective of parents, who are highly involved in transition preparation. We conducted a qualitative thematic analysis of previously conducted semi-structured interviews with 39 parents of 41 autistic adolescents to identify themes related to supports and barriers; we then used Bronfenbrenner's Ecological System's Theory to aid in interpreting the themes. We identified three main supports and four main barriers to the transition to adulthood from the parent interviews. The supports and barriers represent factors to consider at each theorized ecological level. Results point to opportunities to promote person-environment fit and support the transition to adulthood for autistic youth at multiple system levels.