Abstract: Evidence suggests that veterans with posttraumatic stress disorder (PTSD) have a poorer treatment response than nonveterans. In this study, we explored heterogeneity in treatment response for 960 veterans in the United Kingdom with PTSD who had been offered a residential intervention consisting of a mixture of group sessions and individual trauma-focused cognitive behavioral therapy (TF–CBT). The primary outcome was PTSD score on the Impact of Event Scale–Revised (IES–R). Covariates included depression, anxiety, anger, alcohol misuse, functional impairment, and sociodemographic characteristics. Follow-up occurred posttreatment at set time points for 12 months. We present predictors of PTSD severity at posttreatment and follow-up obtained using a latent class growth analysis to identify different treatment trajectories. Multinomial logistic regression models were used to identify covariates predicting class membership, and five classes were identified. Of participants, 71.3% belonged to three classes showing positive treatment responses, and 1.2% showed initial improvement but later relapsed. Additionally, 27.5% of participants were identified within a treatment-resistant class that showed little change in severity of presentation. Depression, anxiety, and having had a combat role during military service increased the likelihood of membership in the treatment-resistant class, odds ratios (ORs) = 1.12–1.53, 1.16–1.32, and 2.89, respectively. Additionally, participants in the treatment-resistant class had higher pretreatment PTSD scores for reexperiencing, avoidance, and hyperarousal symptoms, ORs = 5.24, 2.62, and 3.86, respectively. Findings suggest the importance of triaging individuals and offering interventions tailored to severity of presentation.