While the potential for non-invasive brain stimulation is exciting, research is needed to determine the safety, feasibility, and benefits of non-invasive brain stimulation in human subjects with PTSD. Towards this end, the study team will conduct a single-blind randomized controlled pilot study of transcranial direct current stimulation (tDCS) vs. a sham condition in a sample of 40 adults with PTSD receiving 5 weekly sessions of Written Exposure Therapy (WET), an exposure-based, behavioral psychotherapy for PTSD.