A patient's delusions and/or hallucinations can sometimes be traced to a medical condition other than schizophrenia. Dozens of medical conditions, ranging from neurological disorders to hormonal disruptions to metabolic diseases, can result in psychosis. Doctors must show that the symptoms are directly related to the physical abnormalities created by the medical condition. They can do this by using blood tests, a physical examination, and a detailed history of the patient's past health. Other psychiatric conditions that involve psychosis must also be eliminated. If a patient is aware that a hallucination is not real, this diagnosis is not applicable.

The DSM-IV implies that there may be more cases of psychotic disorder due to a general medical condition than doctors know about. It is difficult to know exactly how widespread it is because it occurs across so many medical specialties. Many of those affected may be treated by physicians who are not psychiatrists.

It is vital to seek an accurate diagnosis of and appropriate treatment for any instance of psychosis, including schizophrenia. Few causes of psychotic symptoms go away on their own, and it should never be assumed they will. Left untended, they can lead to years of suffering and mental decline.