Rumination has been shown to be important in both the maintenance and severity of posttraumatic stress disorder (PTSD) and major depressive disorder (MDD). Increased rumination has also been linked to perceptions of increased stress, which in turn are significantly associated with increased PTSD severity. The present study sought to examine this relationship in more detail by means of a mediation analysis. Forty-nine female survivors of interpersonal violence who met Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM-IV-TR) criteria for PTSD were administered the Clinician-Administered PTSD Scale (CAPS), the Ruminative Thought Style Questionnaire (RTS), the Perceived Stress Scale (PSS), and the Beck Depression Inventory–II (BDI-II). Results indicated that perceived stress mediates the relationship between rumination and PTSD, but did not do so after controlling for depression. Such results provide further evidence for the overlap between PTSD and MDD, and, in broader clinical practice, translate to a sharper focus on rumination and perceived stress as maintenance factors in both disorders.