With the aim of reaching a new classification of psychoses with multiple sclerosis we reviewed the twentieth century literature for observations with regard to the subject, as well as 688 medical records of our patients, looking for the occurrence of paranoid and hallucinatory psychoses in the course of multiple sclerosis. Special attention was paid to the occurrence of cycloid psychoses. With multiple sclerosis, psychoses on the whole--but cycloid psychoses in particular--occur more frequently than in the general population. Women are affected just as frequently as men. Cycloid psychoses occur earlier in the course of the multiple sclerosis than the other psychoses; here, hallucinations occur with a higher frequency. Similar as in the case of HIV-infection, multiple sclerosis can act as a trigger of a cycloid psychosis. The results of our study indicate that men and women experience this disease as similarly threatening. A shortcoming of critical faculties based on the organic disease is an additional factor that favours the outbreak of such a psychosis.