Since its formal introduction into psychiatric nomenclature more than a decade ago, the diagnosis of posttraumatic stress disorder (PTSD) has become firmly entrenched in the legal landscape. In part, this is because PTSD seems easy to understand. It is one of only a few mental disorders for which the psychiatric Diagnostic and Statistical Manual (DSM) describes a known cause. Since the diagnosis is usually based on patients' self-report, however, it creates the possibility of distortion aimed at avoidance of criminal punishment, and, as a result, has achieved mixed success as a criminal defense. When providing expert testimony, mental health witnesses must take care to distinguish between mere PTSD and a causal connection between PTSD and the criminal act in question. PTSD has not only been used to abrogate or diminish responsibility, but also to arrange pre-trial plea bargaining agreements or play a role in sentencing determinations. The author explores various uses and potential abuses of PTSD in criminal jurisprudence and offers suggestions regarding retrospective PTSD assessment.