Permanent diabetes insipidus following head trauma is uncommon, but potentially fatal. The neurologic, roentgenographic, and endocrinologic findings in ten patients with this condition are reported. Eight of the patients were males under the age of 35 years. Unconsciousness (nine) and skull fracture (seven) were frequent findings. Cranial nerve damage (four) and anterior pituitary hormone deficiency requiring replacement (one) were less frequent. An automobile accident caused the trauma in six patients. Standard water deprivation tests revealed that five of the patients had total deficiency of antidiuretic hormone (ADH), and the other five had partial deficiency. The diagnosis of diabetes insipidus was markedly simplified by using a new screening test based on comparing urine and plasma osmolality in candidates with those of normal subjects.