Autism is a complex neurobiological disorder of development that lasts throughout a person’s life.  It is sometimes called a developmental disability because it usually starts before age three, in the developmental period, and because it causes delays or problems in many different skills that arise from infancy to adulthood. 

The main signs and symptoms of autism involve¹ language, social behavior, and behaviors concerning objects and routines:

• Communication—both verbal (spoken) and non-verbal (unspoken, such as pointing, eye contact, or smiling)
• Social interactions—such as sharing emotions, understanding how others think and feel (sometimes called empathy), and holding a conversation, as well as the amount of time a person spends interacting with others
• Routines or repetitive behaviors—often called stereotyped behaviors, such as repeating words or actions over and over, obsessively following routines or schedules, or playing with toys or objects in repetitive and sometimes inappropriate ways, or having very specific and inflexible ways of arranging items

People with autism might have problems talking with you, or they might not want to look you in the eye when you talk to them.  They may have to line up their pencils before they can pay attention, or they may say the same sentence again and again to calm themselves down.  They may flap their arms to tell you they are happy, or they might hurt themselves to tell you they are not.  Some people with autism never learn how to talk.  These behaviors not only make life difficult for people who have autism, but also take a toll on their families, their health care providers, their teachers, and anyone who comes in contact with them.

Because different people with autism can have very different features or symptoms, health care providers think of autism as a “spectrum” disorder—a group of disorders with a range of similar features.  Based on their specific strengths and weaknesses, people with autism spectrum disorders (ASDs) may have mild symptoms or more serious symptoms, but they all have an ASD.  This fact sheet uses the terms “ASD” and “autism” to mean the same thing.

What conditions are in the ASD category?

Currently, the ASD category includes:

• Autistic disorder (also called “classic” autism)
• Asperger syndrome
• Pervasive Developmental Disorder Not Otherwise Specified or atypical autism

In some cases, health care professionals use a broader term—pervasive developmental disorders (PDD)—to describe autism. The PDD category includes the ASDs mentioned above and: Childhood disintegrative disorder, and Rett syndrome. 

Depending on specific symptoms, a person with autism may fall into the ASD or the PDD category. Sometimes, the terms “ASD” and “PDD” are used to mean the same thing because autism is in both categories.