MDMA is an investigational drug that was studied in a randomized, placebo-controlled study in 21 participants, and it included a final evaluation of symptoms at least one year after taking part in the study. While PTSD symptoms in most study subjects stayed at the same levels from when they completed the study, symptoms had returned in a few people. This open-label study is intended to see if an additional MDMA-assisted session conducted at least 14 months after the first sessions can help reduce PTSD symptoms.