Schizophrenia and schizoaffective disorder are similar serious mental illnesses. People haven't really heard of schizoaffective disorder. I usuaully say either "bipolar disorder" or "schizophrenia." That is partially true; schizoaffective disorder is a mix of the two.
Here are the main differences:
1. Mood Symptoms
People with schizoaffective disorder have mood symptoms (depression or mania) in addition to the psychotic symptoms. To be diagnosed schizoaffective, we have to have mood symptoms for 50 percent of the duration of the illness.
Schizophrenia patients can have some mood symptoms, but they don't last long.
2. Psychotic Symptoms
The psychotic symptoms (hallucinations, paranoia, etc) don't last as long for schizoaffective patients. They also tend to come and go. With schizophrenia patients, the psychotic symptoms tend to persist. In schizoaffective disorder, the psychotic symptoms and mood symptoms don't generally mix.
Schizophrenic patients mostly rely on anti-psychotic medicines. With schizoaffective disorder, we may require anti-depressants and/or mood stabilizers to deal with the mood symptoms of the illness.