Objective: To determine whether weak transcranial direct current stimulation (tDCS), which is an interesting new tool inducing prolonged cortical excitability shifts in humans, induces brain edema, disturbance of the blood-brain barrier or structural alterations of the brain detectable by magnetic resonance imaging (MRI).Methods: In 10 healthy individuals, tDCS, which is known to alter cortical excitability for about 1 h, was applied over motor and pre-frontal cortices. Contrast-enhanced T1-, T2-, and diffusion-weighted MRI was performed immediately before, 30 and 60 min after tDCS.Results: MRI performed 30 and 60 min after tDCS did not show pathological signal alterations in pre- and post-contrast-enhanced T1-weighted and diffusion-weighted MR sequences.Conclusions: tDCS protocols which are known to result in cortical excitability changes persisting for an hour after stimulation do not induce brain edema or alterations of the blood-brain barrier or cerebral tissue detectable by MRI.Significance: These results deliver further evidence for the safety of the currently applied tDCS protocols in humans.