Background. Fatigue is a common, persistent complaint following traumatic brain injury (TBI). Effective treatment is not well established. Objective. The current study aimed to investigate the efficacy of 4 weeks of light therapy for fatigue in patients with TBI. Methods. We undertook a randomized, placebo-controlled study of 4-week, 45 min/morning, home-based treatment with short wavelength (blue) light therapy ((max) = 465 nm, 84.8 mu W/cm(2), 39.5 lux, 1.74 x 10(14) photons/cm(2)/s) compared with yellow light therapy ((max) = 574 nm, 18.5 mu W/cm(2), 68 lux, 1.21 x 10(12) photons/cm(2)/s) containing less photons in the short wavelength range and a no treatment control group (n = 10 per group) in patients with TBI who self-reported fatigue and/or sleep disturbance. Assessments of fatigue and secondary outcomes (self-reported daytime sleepiness, depression, sleep quality, and sustained attention) were conducted over 10 weeks at baseline (week -2), midway through and at the end of light therapy (weeks 2 and 4), and 4 weeks following cessation of light therapy (week 8). Results. After controlling age, gender, and baseline depression, treatment with high-intensity blue light therapy resulted in reduced fatigue and daytime sleepiness during the treatment phase, with evidence of a trend toward baseline levels 4 weeks after treatment cessation. These changes were not observed with lower-intensity yellow light therapy or no treatment control conditions. There was also no significant treatment effect observed for self-reported depression or psychomotor vigilance performance. Conclusions. Blue light therapy appears to be effective in alleviating fatigue and daytime sleepiness following TBI and may offer a noninvasive, safe, and nonpharmacological alternative to current treatments.