Adulthood autism diagnosis has become increasingly common, but little is known about post-diagnosis support experiences and needs. We interviewed 19 autistic adults and 4 support persons on experiences of formal and informal post-diagnosis support. Reflexive thematic analysis was used to identify themes. Participants reported difficulties accessing suitable formal support, especially regarding education and employment. Informal support was helpful but created challenges in the relationships between autistic adults and support persons. For autistic adults, support from autistic peers fostered belonging and self-acceptance. We also identified complex interactions between adults' post-diagnosis identity development and support experiences as they resolved the dilemma between self-acceptance and a desire to change. Findings have important implications for services working with autistic adults and their families.