Book excerpt: This book explains in detail the diagnosis, management, and treatment of comorbid disorders in patients with autism spectrum disorders (ASD). Important insights are provided into the nature of the symptoms of psychiatric comorbidities in these patients, and particularly children and adolescents, with a view to assisting clinicians in reaching a correct diagnosis that will permit the implementation of appropriate treatment strategies, whether psychological or pharmacological. The full range of potential comorbidities is considered, including mood disorders, anxiety disorders, obsessive-compulsive disorder, schizophrenia spectrum and other psychotic disorders, eating disorders, disruptive behavioral disorders, Tourette’s disorder, and substance-related disorders. In each case guidance is provided on how to avoid incorrectly attributing symptoms to ASD and on treatment options. Psychiatric Comorbidities in Autism Spectrum Disorders will be of value to all practitioners who are confronted by patients with these complex co-occurring conditions.