Schizophrenia is type of mental disorder that is characterized by abnormal behavior and the inability to identify what is real and what is not. Schizophrenia often causes people to hear voices, see things that are not there, have hallucinations and delusions, and overall experience a very abnormal way of thinking or behaving. Schizophrenia may also be known as paranoid schizophrenia. It is estimated that about one percent of people in the world have schizophrenia.