A growing awareness of posttraumatic stress disorder has led to recent use of the disorder as a legal defense against criminal responsibility for both violent and nonviolent crimes. Diagnosis of posttraumatic stress disorder is difficult because the symptoms are mostly subjective, often nonspecific, usually well publicized, and, therefore, relatively easy to imitate. Accurate psychiatric testimony in such cases requires diligent searching for collateral sources of information. The authors argue that the insanity defense is appropriate only in the rare instance that a dissociative episode related to posttraumatic stress disorder directly leads to criminal activity.