Post‐traumatic Stress Disorder (PTSD) is a psychiatric diagnosis that links a stressor to an anxiety reaction. It is increasingly the subject of compensation claims in Australian courts. A recent Federal Court decision ruled against an applicant's claim for PTSD arising from exposure to atomic testing in Maralinga in 1957. The legal definition of stressor is discussed in the context of this case and of recent developments in diagnostic criteria of PTSD. Forensic psychologists need to be aware that ambiguities still exist in the definition of stressor, and that a legal definition has yet to be stipulated in Australian court