The study aimed to explore predictors of treatment effectiveness in a sample of 79 children with ASD who received cognitive behavioral therapy (CBT) for their anxiety disorders. Severity of anxiety disorders and anxiety symptoms were used to measure treatment effectiveness and was assessed pre-treatment, post-treatment, 3 months-, 1 and 2 years after CBT. Child characteristics and maternal anxiety did not predict treatment effect. Children with anxious fathers and children in "un-involved" families had less anxiety symptoms at pre-treatment and displayed a less steep decline. Children from "authoritarian" families showed higher pre-treatment anxiety levels but responded quite well to treatment. Findings stress the importance of parent (father) and family factors in the treatment of anxiety disorders in youth with ASD.