Question Does repeated anodal transcranial direct current stimulation (A-tDCS) of the left dorso-lateral prefrontal cortex (DLPFC) enhance cognitive rehabilitation effects on memory and attention in patients with traumatic brain injury (TBI). Methods Twenty-three adult patients, 4–92months post severe TBI, were randomly allocated to two groups. The experimental group received A-tDCS (10min; 1mA; in the DLPFC), followed by 1-h cognitive training, daily for 15days. Controls received A-tDCS for 25s (sham condition) with the same rehabilitation programme. Effects of the treatment were assessed using a battery of memory and attention tests (Rey’s Auditory Verbal Learning Test, Paced Auditory Serial Addition Test, Cambridge Neuropsychological Test Automated Battery), which included visual and auditory modalities. Additionally, European Brain Injury Questionaire was used to assess functional gains in daily activities. Participants were tested twice before beginning rehabilitation (to control for spontaneous recovery), after rehabilitation completion, and four months later. Results Tests scores in both groups were similar at three weeks before and immediately before treatment. After treatment, the experimental group exhibited larger effect sizes in six out of eight cognitive outcome measures, but they were not significantly different from controls. At follow-up, experimental group’s effect sizes were higher in five outcome measures. However, differences remained insignificant. No serious adverse effects were observed during the programme. Conclusion In contrast to previous studies, our study did not provide sufficiently strong evidence to support the efficacy of repeated A-tDCS over the left DLPFC for enhancing rehabilitation of memory and attention in patients after severe TBI. However, effect sizes suggested a positive response to stimulation.