Sleep disturbance plays a significant role in cognitive impairment following traumatic brain injury (TBI). To summarize recent findings that examine sleep disturbance and cognition in TBI. Epidemiological information on sleep disorders in people with TBI is presented. A simple introduction to the role of sleep in normal cognition provides context for the literature on clinical populations. Current theory on the mechanisms underlying cognitive problems in people with sleep disorder is briefly described. Findings on the relationship between sleep disorder and cognitive problems in TBI is examined in more detail. Consistent reports of an association between sleep duration and cognition include several studies noting positive associations (shorter sleep duration accompanies cognitive impairment) and others observing negative associations (longer sleep duration accompanies cognitive problems). Both insomnia and hypersomnolence are forms of sleep disturbance that disrupt key mental processes such as memory consolidation. Obstructive sleep apnea, cerebral structural abnormalities, neurochemical changes and psychiatric pathology are implicated. Additional information is needed on how severity of injury impacts sleep and cognition. Hypothesized mechanisms underlying the effects of sleep on cognition in TBI should be empirically tested. Further, discrepancies between objective and subjective measures of sleep and cognition must be explored.