AbstractAn effectiveness trial found that telemedicine collaborative care for posttraumatic stress disorder (PTSD) significantly increased engagement in trauma‐focused psychotherapy (TFP) and improved PTSD symptoms. However, in a subsequent implementation trial, very few veterans enrolled in collaborative care initiated TFP. We conducted a mixed‐methods evaluation to determine why veterans did not initiate TFP in the implementation trial. After conducting chart reviews of 1,071 veterans with PTSD enrolled in collaborative care, patients were categorized into four mutually exclusive TFP groups: TFP not discussed; TFP discussed, declined; TFP discussed, did not decline; and TFP initiated. We conducted semistructured interviews with 43 unique patients and 58 unique providers (i.e., care managers and mental health specialists). Almost half (48.6%) of the veterans had no documentation of discussing TFP with their care manager; another 28.9% discussed it but declined. Most veterans (77.1%) had an encounter with a mental health specialist, 36.8% of whom never discussed TFP, and 35.7% of whom discussed it but declined. Providers reported that many veterans were not able, willing, or ready to engage in TFP and that non–trauma‐focused therapies were better aligned with their treatment goals. Veterans gave numerous reasons for not initiating TFP, including having bad prior experiences with TFP and wanting to avoid thinking about past traumatic experiences.Commonly cited reasons for noninitiation were providers never discussing TFP with veterans and veterans declining TFP after discussing it with their provider. Interventions, such as shared decision‐making tools, may be needed to engage providers and patients in informed discussions about TFP.