Purpose: Social anhedonia is a transdiagnostic trait that reflects reduced pleasure from social interaction. It has historically been associated with autism, however, very few studies have directly examined behavioral symptoms of social anhedonia in autistic youth. We investigated rates of social anhedonia in autistic compared to non-autistic youth and the relative contributions of autism and social anhedonia symptoms to co-occurring mental health. Methods: Participants were 290 youth (M[subscript age]=13.75, N[subscript autistic]=155) ranging in age from 8 to 18. Youth completed a cognitive assessment and a diagnostic interview. Their caregiver completed questionnaires regarding symptoms of autism and co-occurring psychiatric conditions. Results: Autistic youth were more likely to meet criteria for social anhedonia than non-autistic youth. There was a significant positive relationship between age and social anhedonia symptom severity, but there was no association between sex and social anhedonia. Dominance analysis revealed that social anhedonia symptom severity had the strongest association with symptoms of depression and social anxiety, while symptoms of ADHD, generalized anxiety, and separation anxiety were most strongly associated with autism symptom severity. Conclusion: This was the first study to tease out the relative importance of social anhedonia and autism symptoms in understanding psychiatric symptoms in autistic youth. Findings revealed higher rates of social anhedonia in autistic youth. Our results indicate that social anhedonia is an important transdiagnostic trait that plays a unique role in understanding co-occurring depression and social anxiety in autistic youth. Future research should utilize longitudinal data to test the transactional relationships between social anhedonia and internalizing symptoms over time.