The course of dementia of old age is inpredictable for an important part. It is not possible to differentiate between groups of patients characterized by a specific course of the disease. Moreover there is found a remarkable variability between individual patients. The course of the disease in certainly not characterized by a gradual decline. The disease has a tendency towards a marked stability. Improvements are always possible till the end. These improvements, often without any obvious cause, can be quite important. The disease can in most cases be influenced by therapeutic measures which influence the general activity of the patient. This study became possible by the development of specific behaviour rating scales and psychologica) tests. There is a statistical correlation between these two. Longitudinal studies are of the greatest importante to get a better insight into the course of dementia in the elderly. Some modern views are briefly discussed.