The authors distinguish between two evolutive forms of dementia, one being chracterized by prpgressive deterioration (for instance in the course of arteriopathic, degenerative or infections processes) and the other in which dementia sets in after the clinical picture has improved (for instance after meningeal haemorrhage, craniocerebral injury, endocrinous, metabolic or circulatory disorders, etc.). Ventricular drainage (according to Pudenz-Heyer) was performed in 20 patients presenting dementia: the results were favourable in the seven patients presenting dementia: the results were favourable in the seven patients presenting the first evolutive form and in almost all 13 patients presenting the second form. The pathogenic problems.