Autism and OCD (obsessive compulsive disorder) are two very separate and different diagnoses. Autism is a spectrum disorder that is typically discovered in childhood, while OCD is an anxiety disorder that can present at any age. Although the symptoms might at first seem similar, it is fairly easy to distinguish between them once you know what to look for.
Understand that both autism and OCD are characterized by obsessions and compulsions. Obsessions are thoughts that plague the patient on a regular basis, often with clockwork regularity, while compulsions are behaviors that are repeated over and over again and may be triggered by a certain action or experience.
Realize that autism compulsions are usually automatic and unconscious, while OCD compulsions generally are brought on by obsessions. For example, an autism patient might constantly flap his hand back and forth in the air, seemingly without realizing that he is doing it, while an OCD patient will deliberately wash his hands exactly 24 times each day.
Know that autism has been strongly linked to genetic components, while OCD is often a response to life experiences. Post-traumatic stress disorder, for example, can cause a patient to develop OCD as a way to deal with stress and anxiety. Autism, however, is usually present from birth, though symptoms might not become clear for several years.
Observe the way that autism and OCD patients handle their symptoms. In most cases, those with OCD experience depression and anxiety because they feel different, or out of frustration with their compulsions and obsessions. Autistic patients, on the other hand, are generally more comfortable with their conditions and less likely to feel depressed about it.
Understand that the social implications of autism and OCD are much different. Autistic patients have difficulty connecting to people, and may become overwhelmed in social situations. They may bond with only one or two people over the course of their entire lives, and sometimes will reject the affections of others. OCD patients, however, can develop healthy and normal relationships, though they are sometimes plagued with paranoia that can complicate social interaction.
Realize that most autism patients suffer from internalized obsessions, while OCD patients suffer from external obsessions. For example, an autistic individual might be obsessed with counting or finding synonyms to words, either silently or out loud, while someone with OCD might fear leaving the house, becoming violent or becoming contaminated with germs.