This is a study of comorbid anxiety disorders and how they affect the clinical picture of comorbid cases. The sample consisted of 576 Spanish children aged 8 to 17 years receiving psychiatric outpatient consultation that were evaluated using a semi-structured diagnostic interview for both parents and children. A specific association of homotypic comorbidity among anxiety disorders that was independent of the presence of other disorders was found. There was heterotypic comorbidity between anxiety and depressive disorders, ADHD, anorexia and tic disorders. Relationships between non-anxiety disorders were, in general, independent of anxiety, but anxiety moderated the relationship between ADHD-Conduct disorder and Conduct disorder-enuresis. Comorbid anxiety increased difficulties in social interaction, was related with higher global impairment and had an impact on consultation and medication. Anxiety disorder comorbidity should be well recognized in order not to disregard the treatment of all present disorders.