Acquired brain injury (ABI) can result in devastating and long-lasting disabilities in the physical, cognitive, psychological and social domains of life. The Department of Health (2005) estimates that, in the United Kingdom, there are 420,000 people aged between 16 and 65 years living with a traumatic brain injury (TBI) and that many more people are affected by non-traumatic types of brain injury. Fatigue is one of the most frequently reported symptoms, even among those with mild to moderate injuries (Lezak et al 2004). Significant numbers of people are affected by fatigue for many years following a TBI and it is a substantial but understudied issue for people with other types of ABI, such as stroke (Choi-Kwon et al 2005). Van der Naalt et al (1999) found fatigue to be prevalent in 57% at 1 month, 61% at 3 months, 45% at 6 months and 45% at 12 months post mild-moderate TBI. Olver et al (1996) reported a rate of 73% of participants experiencing fatigue at 5 years following TBI. The underlying physiological mechanisms that cause excessive fatigue following ABI are currently poorly understood. Multiple factors are implicated, including mood disturbance, endocrine factors, sleep disturbance, nutrition, medication side effects, decreased physical fitness and cognitive dysfunction, such as slowed speed of processing and