BACKGROUND AND PURPOSE: A number of neuro-stimulants are routinely used as part of post-acute care of hospitalized brain-injured patients. To our knowledge, the effect of these stimulants on the sleep-wake cycles of brain-injured patients undergoing rehabilitation has not been addressed. We examined the effect of one of the most commonly used neuro-stimulants, methylphenidate, on the sleep-wake behavior of brain-injured patients undergoing rehabilitation at a dedicated brain injury clinic. PATIENTS AND METHOD: For this study, records of patients admitted between January and December 1999 were scrutinized retrospectively for the data on observationally defined sleep-wake distribution. A total of 30 patients diagnosed with traumatic brain injury were identified as having been observed for a full 24h a day for at least 10 days. Some of these patients (n=17) were administered methylphenidate on clinical grounds. They served as the experimental group, while the unmedicated patients (n=13) served as controls. For the present analysis, the sleep-wake cycles were arbitrarily designated as nighttime and daytime, respectively. A cumulative sleep-wake quantity in a 24-h period was also observed. RESULT: The average number of hours of sleep during a 24-h period was not significantly different for the two cohorts. Similar trends emerged for the nighttime and daytime observations. On the whole, methylphenidate appears not to have unfavorable effects on sleep-wake cycles, presently defined as nighttime, daytime and 24-h, in the traumatic brain injury population. CONCLUSION: This study sought to gain better understanding of the effect of methylphenidate on daytime sleepiness and nighttime sleep, and the data suggest that administration of methylphenidate does not appear to have an adverse effect on sleep-wake quantity.