Abstract: Prior studies on individuals with posttraumatic stress disorder (PTSD) defined an adequate dose of psychotherapy as receiving at least nine sessions within a 15-week period. Yet, few studies have examined whether this definition of adequate dose is associated with meaningful change in PTSD symptoms over an extended period. To examine whether an adequate dose of individual or group psychotherapy was associated with PTSD symptom improvement, we identified mental health outpatient visits in the electronic medical record for a cohort of veterans enrolled in Veterans Health Administration (VHA) services (N = 1,649) across 5 years. Using latent growth curve modeling, we estimated the effect of receiving an adequate dose of psychotherapy on the PTSD symptom course. Among the sample, 992 participants (60.16%) received at least one individual therapy session and 506 participants (30.7%) received at least one group therapy session; of those, 226 (22.78%) received an adequate dose of individual therapy and 212 (41.9%) received an adequate dose of group therapy, respectively. An adequate individual therapy dose, but not group therapy dose, was associated with a decrease in PTSD Checklist for DSM-5 (PCL-5) scores over time. This improvement was extremely gradual (average of 1.57 PCL-5 point decrease per year). Adequate dose of psychotherapy, defined as nine sessions of routine psychotherapy over 15 weeks, is associated with minimal symptom change. This suggests that commonly used definitions of adequate dose have minimal clinical utility.