Using the criteria of the Structured Clinical Interview for DSM-III-R Dissociative Disorders (SCID-D), we assessed the incidence of feelings of unreality among a sample of 70 persons who had sustained head injuries. Among those whose head trauma could be classfied as mild, more than 60% complained of a depersonalization syndrome. Among those with a significant period of unconsciousness, only 11% had similar complaints. There was a high comorbidity with post-traumatic stress disorder and vertigo. Feelings of unreality were not associated with cognitive impairment or elevated personality test scores, nor were there significant relationships with gender or involvement in litigation. A conservative estimate of incidence of depersonalization among persons with minor head trauma is 13%, while, at the upper end, as many as 67% of persons who sustain mild head injury may experience feelings of unreality.