We report on the case of a 57-year-old man who experienced an episode of hypomania while participating in a clinical trial of transcranial direct current stimulation for the treatment of major depressive disorder. Although hypomania and mania have been reported after transcranial magnetic stimulation to the dorsolateral prefrontal cortex in the past, to our knowledge, this is the first report of mania after transcranial direct current stimulation to the dorsolateral prefrontal cortex.