There is a nosologic difference between the French schizophrenia and the English schizophrenia which include all chronic delusions. A genetic study of chronic delusions, based on the rules of the French nosology, has two goals: to clarify their genetic etiology, and to test those nosologic differences. This study was made on the families of 45 patients with chronic delusions. The conclusions are: the ‘délires paranoïaques chroniques’ have a genetic etiology and are related to schizophrenia; the ‘psychoses hallucinatoires chroniques’ are not influenced by the genetic etiology and are not related to schizophrenia. Therefore, the ‘psychoses hallucinatoires chroniques’ constitute an autonomic entity according to the French nosology.