One of the difficulties in defining schizophrenia is the possibility of its heterogeneity. Schizophrenia may be divided into organic and idiopathic on the basis of precipitating factors; the difference between the two is supported by evidence from family studies and differences in symptomatology. A further division of idiopathic schizophrenia may be made into typical and atypical schizophrenia based on differences in clinical features, family history, mode of inheritance, and prognosis. There is suggestive evidence that within typical schizophrenia, paranoid and nonparanoid subtypes may be idstinguished due to clinical and family differences. Within nonparanoid schizophrenia, simple, catatonic, and hebephrenic schizophrenia may also prove to be distinct entities. The available evidence for differentiating the subtypes of typical schizophrenia is inconclusive to date. However, several recent developments in the methodology of family research may lead to more convincing findings for differentiating subtypes within typical schizophrenia.