Prolonged exposure, a cognitive behavioral therapy including both in vivo and imaginal exposure to the traumatic memory, is one of several empirically supported treatments for chronic posttraumatic stress disorder (PTSD). In this article, we provide a case illustration in which this well-validated treatment did not yield expected clinical gains for a client with PTSD and co-occurring major depression. After providing an overview of the literature, theory, and treatment protocol, we discuss the clinical cascade effect that underlying ruminative processes had on the treatment of this case. Specifically, we highlight how ruminative processes, focusing on trying to understand why the traumatic event happened and why the client was still suffering, resulted in profound emotional distress in session and in a lack of an "optimal dose" of exposure during treatment. (Contains 1 figure.)