Background: Social anxiety disorder (SAD) is common in youths. However, our understanding of SAD in children is inferior to that of SAD in adolescents or adults, and it is unclear if known adult SAD maintenance mechanisms may also operate in children with SAD. Aim: The paper sets out to investigate the specificity of positive automatic thoughts, social threat negative automatic thoughts, repetitive negative thinking, positive and negative metacognitions in predicting SAD symptoms and diagnoses in clinically anxious children. Method: We enrolled 122 clinically anxious children aged 7-13 years; of these, 33 had an SAD diagnosis. Results: SAD symptoms correlated positively with social threat negative automatic thoughts, repetitive negative thinking, and negative metacognitions, and negatively with positive automatic thoughts. Linear regression indicated that, of these variables, only social threat negative automatic thoughts predicted social anxiety symptoms. Logistic regression indicated that social threat negative automatic thoughts, a higher number of diagnoses and negative metacognitive beliefs specifically predicted the presence of SAD diagnosis. Conclusions: Our findings suggest that content-specific social threat negative automatic thoughts was the only variable that specifically distinguished both higher levels of social anxiety symptoms and diagnoses.