To explore the presence and types of sleep disorders in chronic patients with severe traumatic brain injury (TBI) undergoing inpatient rehabilitation using formal diagnostic criteria based on the International Classification of Sleep Disorders, 2nd edition. Cross-sectional study. Inpatient brain injury rehabilitation units. Chronic inpatients with severe TBI (N=30) were evaluated during rehabilitation. Not applicable. Participants wore an actiwatch for 7 days and completed self-report measures on sleep, mood, fatigue, pain, and daytime sleepiness. Twenty participants (67%) had a sleep-wake cycle disturbance, of which 15 (50%) met diagnostic criteria for a sleep disorder. Diagnosed sleep disorders in the sample were insomnia (26.7%), posttraumatic hypersomnia (6.7%), delayed sleep phase syndrome (10%), irregular sleep-wake pattern disorder (3.3%), and periodic limb movement disorder (3.3%). Sleep quality was estimated by senior clinical staff as interfering with rehabilitation in 36.6% of the sample. Poor sleep quality was associated with greater anxiety, fatigue, and daytime sleepiness. Consistent with previous studies, the present study showed high levels of sleep-wake cycle disturbances in patients with severe TBI undergoing rehabilitation, which were associated with anxiety, fatigue, and daytime sleepiness. These findings highlight the importance of assessing and treating sleep problems in patients with TBI undergoing rehabilitation. Copyright © 2015 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.