Posttraumatic stress disorder (PTSD) can occur after a traumatic experience and can cause severe symptoms that interfere with a person's psychological, physical, interpersonal, occupational, and social functioning. It is important to accurately identify genuine cases of PTSD and, as part of the differential diagnosis, to rule out instances of false PTSD. False PTSD diagnoses can adversely affect treatment planning, resource management, and research. The subjective nature of stressors, stereotypic presentation of symptoms, wealth of resources detailing how to malinger PTSD, and the high stakes for individuals involved in criminal, civil, and disability evaluations create challenges for making an accurate diagnosis. This article presents a systematic approach to help clinicians and forensic evaluators distinguish genuine PTSD from false variants of the disorder. It describes the types of false PTSD to be considered as alternative diagnoses, including malingered PTSD (for external gain, such as receiving a disability pension or evading criminal consequences), factitious PTSD (for internal gain, such as assuming the victim or hero/veteran role), and misattributed PTSD (legitimate psychopathology misdiagnosed as PTSD). The authors describe clinical features and psychological testing that may be leveraged to aid in reaching a more valid diagnosis.