A session devoted to personality and neurosurgery will concern the disturbances of personality in neurosurgical diseases and after neurosurgical interventions. Most neurosurgeons would be embarrassed if they had to give a definition of “personality”, because they are neither psychiatrists nor philosophers. But every neurosurgeon and, even, every house doctor knows perfectly well what disturbances of personality mean. All of them have experienced, in their medical practice, that neurological impairment was not necessarily limited to obvious deficiencies like hemiparesis, aphasia etc. Patients who sustained major brain damage followed by recovery, may nevertheless remain afflicted by changes of character with intellectual and mental sequelae that considerably change their “personality”. Let us take the example of a brilliant student or of an eminent scientist, who ultimately recovered from a severe cranio-cerebral injury, but remained merely the shadow of his former self. Let us also consider the example of a man who-recovered from a severe subarachnoid haemorrhage caused by the rupture of an anterior communicating aneurysm and was successfully operated upon. Some time later, he looks in perfect condition, but his relatives may complain that his character, his moral sense, in a word, his “personality” has changed, as a consequence of the disease. Although nowadays aneurysm surgery gives much better results than some years ago, it still cannot avoid either a small amount of postoperative mortality and morbidity, or, above all, the consequences of the bleeding itself.