The concept of deficit schizophrenia is regarded as one of the most promising attempts to reduce heterogeneity within schizophrenia. This paper summarizes the clinical, neurocognitive, brain imaging and electrophysiological correlates of this subtype of schizophrenia. Attempts to identify genetic and non-genetic risk factors are reviewed. Methodological limitations of studies supporting the efficacy of atypical antipsychotics in the treatment of the syndrome are highlighted. Two decades of research on deficit schizophrenia have failed to prove that it represents the extreme end of a severity continuum in schizophrenia, while some findings support the claim that it may be a separate disease entity.