The current trial examined the value of modifying empirically validated treatment for childhood anxiety for application via written materials for parents of anxious children. Two hundred sixty-seven clinically anxious children ages 6-12 years and their parents were randomly allocated to standard group treatment, waitlist, or a bibliotherapy version of treatment for childhood anxiety. In general, parent bibliotherapy demonstrated benefit for children relative to waitlist but was not as efficacious as standard group treatment. Relative to waitlist, use of written materials for parents with no therapist contact resulted in around 15% more children being free of an anxiety disorder diagnosis after 12 and 24 weeks. These results have implications for the dissemination and efficient delivery of empirically validated treatment for childhood anxiety.