This study aimed to explore experiences of support after adulthood autism diagnosis. In this mixed-methods survey study of 137 adults, we found that most common formal supports received were counselling and mental health. Common unmet support needs were sensory sensitivities and accessing other services. Cost, lack of information, and fear of not being taken seriously were common barriers. Informal support was mainly helpful for self-understanding and emotions toward diagnosis. Qualitative findings included difficulties accessing formal support, need for practical quality-of-life supports and support from autistic peers and online communities. Based on these findings, future development of supportive interventions should address unmet needs, improve access, and explore the integration of autistic peer support and online support into formal services.