Various clinical practice guidelines for the treatment of posttraumatic stress disorder (PTSD) have consistently identified two frontline evidence‐based psychotherapies (EBPs)—prolonged exposure (PE) and cognitive processing therapy (CPT)—as well as other empirically supported treatments (EST), such as eye movement desensitization and reprocessing (EMDR) and cognitive therapy for PTSD (CT for PTSD). However, researchers and clinicians continue to be concerned with rates of symptom improvement and patient dropout within these treatments. Recent attempts to address these issues have resulted in intensive, or “massed,” treatments for PTSD. Due to variability among intensive treatments, including treatment delivery format, fidelity to the EST, and the population studied, we conducted a systematic review to summarize and integrate the literature on the impact of intensive treatments on PTSD symptoms. A review of four major databases, with no restrictions regarding publication date, yielded 11 studies that met all inclusion criteria. The individual study findings denoted a large impact of treatment on reduction of PTSD symptoms, ds = 1.15–2.93, and random‐effects modeling revealed a large weighted mean effect of treatment, d = 1.57, 95% CI [1.24, 1.91]. Results from intensive treatments also noted high rates of treatment completion (i.e., 0%–13.6% dropout; 5.51% pooled dropout rate across studies). The findings suggest that intensive delivery of these treatments can be an effective alternative to standard delivery and contribute to improved treatment response and reduced treatment dropout.