Despite well-know semiological characteristics, the nosological position of the late onset hallucinatory-delusional psychosis with respect to schizophrenia is much debated. As regard prognosis factors, the study of 135 cases (36 men, 99 women) has shown that a sudden onset often happens in men, that, however, women often present a mental automatism syndrome, which becomes exceptional with age; finally, that influence phenomena are seldom found in men, especially after the age of 60. Rich and diversified symptoms of mental automatism are often observed in younger patients but they generally do not last. On the contrary, the clinical picture of the very late onset is comparatively simple and restricted; its main symptoms are either hallucinations or delusions and these symptoms tend to remain. Such semiological and evolutive modifications according to the age of the patient may appear in case of recurrence. The analysis of the pathoplastic role of age in the clinical picture leads to an hypothesis: a relation between the two possible evolutions (favourable and unfavourable) of the late onset hallucinatory-delusional psychosis and the two groups (atypical and nuclear) of schizophrenia.