The Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) recognizes life-threatening illness as a potential stressor that can precipitate posttraumatic stress disorder (PTSD). This study represents the first study of PTSD in the context of having a diagnosis of multiple sclerosis (MS). Fifty-eight MS patients were administered the Clinician Administered PTSD Scale, the Geriatric Depression Scale, and Disease Steps Questionnaire. Nine participants (16%) met symptom criteria for PTSD. In terms of those who satisfied the reexperiencing criterion, 75% of participants reported intrusions related to future-oriented concerns about their prognosis. These findings suggest that a significant proportion of MS patients experience PTSD-type reactions. These results are discussed in terms of the suitability of the PTSD framework to account for the distinctive nature of stress reactions secondary to life-threatening illness.