The main signs and symptoms of autism in adults are impairment in social interactions and communication along with a person's behavior, according to MedicineNet.com. Adults with autism usually do not seek out normal social interactions, play games more suitable for younger people, and may repeat simple phrases back to speakers. Behavioral abnormalities include extreme daily rituals, obsessive organizational skills and systematic actions with the same object.
For instance, someone may tell an adult with autism "Look at the airplane" and then the autistic person responds with "at airplane." MedicineNet.com explains another social interaction includes reciting songs, commercials and television shows for no apparent reason.
An example of ritualistic behavior is when an autistic adult requires the exact same amount of bath water every time. Another way this symptom manifests itself is when an adult lines up clothes, repeatedly and systematically, by moving each individual piece in the same manner, according to MedicineNet.com.
WebMD states one symptom of autism in adults is an inability to live completely independent. This symptom depends on the intelligence level of an adult with autism. At least 33 percent of adults with autism can live at least partially independent. Some autistic adults live with part-time or full-time supervision. Even adults with autism who live independently may still have trouble relating to their peers.