Anxiety disorders are common in individuals with developmental disabilities (DDs), although they may not be diagnosed and treated as often as they are in patients without DDs. Patients with mental retardation, autism, and other pervasive developmental disorders may exhibit comorbid anxiety disorders, such as generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), phobias, and other anxiety symptoms at much higher rates than in the general population, but identification of these comorbid anxiety disorders may be made more difficult by the presence of the DD and concurrent difficulties with communication, other behavior problems, the lack of standardized assessments specific to diagnosing patients with DDs and psychiatric comorbidities, and the need for greater collateral sources of assessment information. In addition, systematic study of the treatment of anxiety in patients with DD is limited to a relatively small number of empirical studies done specifically in these patients along with case reports and theoretical reviews on the extension and modification of more well-studied treatments used for anxiety in patients without DDs. The present article reviews the literature on the prevalence, features, assessment and diagnosis of anxiety disorders in individuals with DDs, and also reviews empirical studies of pharmacological and psychological treatment of patients with comorbid anxiety and DD and summarizes the findings. Recommendations are made to guide treatment and further research in this area.