Schizophrenia is a mental illness.
Affected individuals have delusions, hallucinations, and overall functioning below average. In mental retardation, low social functioning, odd behavior and low affect may suggest schizophrenia. One must be sure that these symptoms and the delusions and hallucinations are not the result of communication problems typical in mental retardation. Not all people show all of these symptoms, and some show very few of these. One may have a difficult time keeping the person on topic.