The cerebral amyloïd angiopathy ( AAC) is a disease characterized by deposits of beta-amyloid peptids in the walls of the arteries of young and average calibre of the brain and the leptomeninx. The incidence of the AAC increases strongly with the age and represents a major cause of spontaneous brain haemorrhage to people over 60. The main demonstration is the lobar brain haemorrhage, the other ones are bleedings under arachnoid cortical and microbleedings leading to cognitive decline.