Autism with social anxiety is associated with acquiescent behaviors and enlarged amygdala volume.

Social anxiety (SA) frequently co-occurs with autism spectrum disorder (ASD), but it remains unclear whether SA in ASD reflects greater symptom severity or a distinct subtype. Across two complementary studies, we characterized the behavioral and neural correlates of SA in ASD using a naturalistic social navigation task measuring affiliative and power-related behaviors. In Study 1 (ASD = 575; controls = 357), autistic individuals with SA exhibited significantly reduced task-derived power behaviors (e.g., compliance with others' requests) compared to those without SA-a pattern not observed in non-autistic individuals. In Study 2 (ASD = 72; controls = 72), individuals with both ASD and SA showed enlarged amygdala volumes relative to both ASD without SA and non-autistic individuals. These behavioral and neural differences found in Study 1 and Study 2 were not observed in ASD with co-occurring depression or generalized anxiety disorder. Moreover, in Study 2, larger amygdala volume in the ASD group was associated with reduced task-derived power behaviors, indicating a neural signature linking social-behavioral differences and anxiety-related features. Together, these findings point to a distinct ASD phenotype marked by social anxiety, altered interpersonal dynamics, and amygdala enlargement, with implications for diagnosis and tailored intervention.