When people refer to “Autism” today, they are usually talking about Autism Spectrum Disorders (ASD), which are five complex, brain-based disorders that affect a person’s behavior as well as social and communication skills. The Centers for Disease Control describes ASDs as:  "developmental disabilities that cause substantial impairments in social interaction and communication and the presence of unusual behaviors and interests. Many people with ASDs also have unusual ways of learning, paying attention, and reacting to different sensations. The thinking and learning abilities of people with ASDs can vary—from gifted to severely challenged. An ASD begins before the age of 3 and lasts throughout a person's life." 

Autism Spectrum Disorders are characterized by significant impairments in social interaction and communication skills, as well as by the presence of extremely challenging behaviors.  Such behaviors include repetitive motor behaviors (hand flapping, body rocking), insistence on sameness, resistance to change and, in some cases, aggression or self-injury. Many individuals with an autism spectrum disorder have significant cognitive impairments, although some have typical or even above average IQs.  30-50% of people with autism also have seizures.

There are five Autism Spectrum Disorders, sometimes called Pervasive Developmental Disorders (PDD):

• PDD-NOS (Pervasive Developmental Delay - Not Otherwise Specified).
• Autism (sometimes referred to as Classic Autism, Early Infantile Autism, Childhood Autism, or Autistic Disorder)
• Asperger Syndrome
• Rett Syndrome
• Childhood Disintegrative Disorder