Residual schizophrenia is a subtype of schizophrenia marked by a presence of 'negative' symptoms (blunted affect, lack of self-care, poor social skills, poor verbal and non-verbal communication) but an absence of the more serious 'positive' symptoms like hallucinations and delusions. Hallucinations and delusions can still be present to some degree to qualify for residual schizophrenia but they must be greatly decreased in severity.
To be diagnosed with residual schizophrenia the patient must have had no 'positive' symptoms (or have them in a very subdued and decreased manner) for at least one year. The patient must still be presenting the 'negative' symptoms typical of schizophrenia. There must be an absence for any other medical explanations for their symptoms like dementia or major depression. Residual schizophrenia can be a transitional period from full-blown schizophrenia to remission or can remain a stable condition for years.