Objective: The goal was to describe the association between post-traumatic stress disorder (PTSD) and in-service sexual harassment in a nationally representative sample of Department of Veterans Affairs PTSD disability applicants. Method: The study was a cross-sectional survey. Results: Of 4,918 eligible veterans, 3,337 (68%) returned surveys. Nonresponse bias appeared to be minimal. After adjustment for other reported traumas, women's reported in-service sexual harassment severity was significantly associated with PTSD symptom severity (p < 0.0001). The effect seen was about the same size as that seen for combat exposure among the men and for in-service sexual assault among the women. Men showed no association between in-service sexual harassment and PTSD (p = 0.33), although power was low for this test. Conclusion: Sexual harassment significantly contributed to female veterans' PTSD symptoms; its contribution to men's symptoms was unclear. We discuss mechanisms through which sexual harassment might affect PTSD symptom severity, including the possibility that sexual harassment sometimes meets the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, definition of a criterion A stressor.