This study is based on 109 patients with severe head injury who had a Glasgow coma score equal to or less than 7 and a Liège coma score equal to or less than 12 in the first 24 hours. The syndrome of inappropriate secretion of antidiuretic hormone seems to us to be a frequent complication of severe craniocerebral trauma. It has been discovered in 33% of our patients. On the other hand, diabetes insipidus was rarely diagnosed (2.8%). We propose, in cranial trauma, to subdivide the syndrome of inappropriate secretion of antidiuretic hormone into two clinical forms: an early syndrome (5%) that becomes apparent towards the second day and is significantly associated with lesions at the base of the skull; and a delayed syndrome that occurs at the end of the first week and is related to different factors inherent in intensive care procedures. Surgical intervention, in the case of acute craniocerebral trauma, does not result in a higher frequency of inappropriate secretion of antidiuretic hormone.