Autistic disorder (autism) is a neuropsychiatric syndrome characterized by marked deficits in reciprocal social relatedness, communication impairment and a narrow range of interests and/or repetitive behaviors. Autism is frequently associated with, but distinct from, mental retardation. It is classified as a subtype of pervasive developmental disorder (PDD) along with 'PDD not otherwise specified' (NOS) and Asperger's disorder. These disorders have in common marked impairments in social relatedness. Individuals with autism may also have other symptoms that become the primary focus of psychiatric treatment. These associated symptoms include aggression, self-injury, irritability and anxiety.