Tinnitus is considered as an auditory phantom percept. Preliminary evidence indicates that transcranial direct current stimulation (tDCS) of the temporo-parietal area might reduce tinnitus. tDCS studies of the prefrontal cortex have been successful in reducing depression, impulsiveness and pain. Recently, it was shown that the prefrontal cortex is important for the integration of sensory and emotional aspects of tinnitus. As such, frontal tDCS might suppress tinnitus as well. In an open label study, a total of 478 tinnitus patients received bilateral tDCS on dorsolateral prefrontal cortex (448 patients anode right, cathode left and 30 anode left, cathode right) for 20 min. Treatment effects were assessed with visual analogue scale for tinnitus intensity and distress. No tinnitus-suppressing effect was found for tDCS with left anode and right cathode. Analyses show that tDCS with right anode and left cathode modulates tinnitus perception in 29.9% of the tinnitus patients. For these responders a significant reduction was found for both tinnitus-related distress and tinnitus intensity. In addition, the amount of suppression for tinnitus-related distress is moderated by an interaction between tinnitus type and tinnitus laterality. This was, however, not the case for tinnitus intensity. Our study supports the involvement of the prefrontal cortex in the pathophysiology of tinnitus.