Abstract Background: The prevalence of sleep problems in head injury (HI) patients in the community is high. Previous research suggests that HI patients with sleep problems require longer stays in rehabilitation units and that arousal disturbance disrupts engagement with rehabilitation activities. The present study explored the prevalence and types of sleep problem in patients with severe HI undergoing inpatient rehabilitation and whether sleep problems affect rehabilitation. Methods: Actigraphy, a semi-structured sleep interview, and validated sleep measures were used to identify sleep problems (n=23). Information on rehabilitation, including percentage of goal achievement, frequency of aggressive behaviour, and engagement was collected retrospectively from staff and rehabilitation notes. Relevant factors including daytime sleepiness, fatigue, mood, and pain were explored. Results: Fifteen participants (65.2%) had sleep problems, of which ten (43.8%) met diagnostic criteria for a sleep disorder, whereas in five cases (21.7%) no potential cause for participants’ sleep problems was identified. Sleep disorders in the sample were insomnia (21.7%), post-traumatic hypersomnia (8.7%), circadian rhythm disorder(8.7%), sleep apnoea (4.3%), periodic limb movement disorder (4.3%), and rhythmic movement disorder (4.3%). Sleep quality was not significantly associated with rehabilitation variables, but was estimated by senior staff as interfering with rehabilitation in 26% of the sample.Poor sleep quality was associated with greater anxiety, fatigue, and daytime sleepiness. Conclusions: The majority of HI patients had sleep problems based on actigraphy and validated sleep measures. Poor sleep was associated with mood and arousal problems. Sleep problems may negatively affect the rehabilitation process and patients’ wellbeing. However, the current study was not sufficiently powered to detect significant associations between sleep and rehabilitation. Due to the small sample size, these results are preliminary.