PDD Not Otherwise Specified, PDDNOS or PDD-NOS is a pervasive developmental disorder in which some symptoms of autism or a similar pervasive developmental disorder can be identified, while other symptoms cannot be. Especially common is difficulty interacting with peers.

The PDD-NOS label is used when a child is considered to be on the autism spectrum, but who does NOT meet all 3 strict criteria for autism according to the Diagnostic and Statistical Manual-Fourth Edition (DSM-IV). These kids are most often considered high functioning because they frequently have IQ scores above 70 and who often have Average or better intelligence.

Some clinicians use PDD-NOS as a "temporary" diagnosis for children under the age of 5, when for whatever reason there is a reluctance to diagnose autism. There are several justifications for this: very young children have limited social interaction and communication skills to begin with, therefore it can be tricky to diagnose milder cases of autism in toddler hood. The unspoken assumption is that by the age of 5, unusual behaviours will either resolve or develop into diagnosable autism. However, some parents view the PDD label as no more than a euphemism for autistic spectrum disorders, problematic because this label makes it more difficult to receive aid for early intervention.

Pervasive developmental disorder

PDD-NOS is a Pervasive developmental disorder or PDD. A pervasive developmental disorder refers to a group of disorders characterized by delays in the development of multiple basic functions including socialization and communication. The most commonly known PDD is autism. Parents may note symptoms of PDD as early as infancy and typically onset is prior to 3 years of age. PDD itself generally does not affect life expectancy.

Symptoms of PDD may include communication problems such as:

• Difficulty using and understanding language
• Difficulty relating to people, objects, and events
• Unusual play with toys and other objects
• Difficulty with changes in routine or familiar surroundings
• Repetitive body movements or behaviour patterns