Writing about traumatic, stressful, or emotional events is known to result in improvements in physical and psychological health. What are the mechanisms that underlie these health benefits? In the present study, undergraduates (n=55) were asked to write about (a) the same traumatic experience, (b) different traumatic experiences, or (c) non-traumatic everyday events, during 3 written disclosure sessions. Results indicated that participants who wrote about the same traumatic experience reported significant reductions in respiratory and neurological symptoms at follow-up assessments compared with the other participants. Moreover, cognitive restructuring contributed to the alleviation of depressive and posttraumatic stress symptoms only when participants wrote about the same traumatic experience. Cognitive restructuring did not have a significant beneficial effect on physical symptoms. These findings suggest that habituation underlies the beneficial effects of expressive writing on physical health, and that habituation is necessary for cognitive restructuring to be effective on psychological health.