Abstract
In a large community sample of young adults, we aimed to investigate the relationship between autism, ADHD and how they interact and symptoms of anxiety and depression. We found that both conditions increased the likelihood of reporting these symptoms but that the effects of autism and ADHD on mental health challenges were independent with limited evidence of an interaction between them. This means that the impact of autism remains the same whether or not ADHD is present and vice versa. However, it is the case that having both conditions increases the likelihood of mental health challenges.