Although fatigue and sleep disturbance are commonly reported following traumatic brain injury (TBI), understanding of their nature and treatment remains limited. OBJECTIVES: This article reviews a series of investigations of the nature and causes of fatigue and sleep disturbance following TBI. METHODS: A large cohort of community-based patients with TBI, recruited from a TBI rehabilitation program, completed measures of subjective fatigue and sleep disturbances, as well as attentional measures. A subgroup of participants completed polysomnography and assessment of dim light melatonin onset. RESULTS: Fatigue and sleep disturbance are common. Both are associated with anxiety, depression, and pain. However, fatigue is also associated with slowed information processing and the need for increased effort in performing tasks. Sleep disturbances contribute to fatigue. Objective sleep studies show reduced sleep efficiency, increased sleep onset latency, and increased time awake after sleep onset. Depression and pain exacerbate but cannot entirely account for these problems. There is increased slow-wave sleep. Individuals with TBI show lower levels of evening melatonin production, associated with less rapid-eye movement sleep. CONCLUSIONS: These findings suggest potential treatments including cognitive behavior therapy supporting lifestyle modifications, pharmacologic treatments with modafinil and melatonin, and light therapy to enhance alertness, vigilance, and mood. Controlled trials of these interventions are needed.