There is a variety. Autism is characterized by three main areas of difficulty. Communication, social interaction, and social imagination. Diagnosis in adulthood can be a mixed blessing. Some people decide that they are happy with self diagnosis and decide not to ask for a formal diagnosis. Some adults with autism may need support with day-to-day living. Seeing a psychiatrist or clinical psychologist may help.
DsM 4. Look for the definition online (dsm 4). If still in doubt, take the patient to be seen by a psychiatrist.