Autism spectrum disorder (ASD) and autism are both general terms for a group of complex disorders of brain development. These disorders are characterized, in varying degrees, by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviors.
Autism appears to have its roots in very early brain development. However, the most obvious signs of autism and symptoms of autism tend to emerge between 2 and 3 years of age. Both children and adults with autism typically show difficulties in verbal and non-verbal communication, social interactions, and leisure or play activities.
Autism Spectrum Disorder has specific diagnostic criteria outlined in the American Psychiatric Association's Diagnostic & Statistical Manual of Mental Disorders (DSM-IV-TR).
Autism Fact Sheet
Asperger Syndrome Fact Sheet