Abstract Over the last two decades, treatment guidelines have become major aids in the delivery of evidence‐based care and improvement of clinical outcomes. The International Society for Traumatic Stress Studies (ISTSS) produced the first guidelines for the prevention and treatment of posttraumatic stress disorder (PTSD) in 2000 and published its latest recommendations, along with position papers on complex PTSD (CPTSD), in November 2018. A rigorous methodology was developed and followed; scoping questions were posed, systematic reviews were undertaken, and 361 randomized controlled trials were included according to the a priori agreed inclusion criteria. In total, 208 meta‐analyses were conducted and used to generate 125 recommendations (101 for adults and 24 for children and adolescents) for specific prevention and treatment interventions, using an agreed definition of clinical importance and recommendation setting algorithm. There were eight strong , eight standard , five low effect , 26 emerging evidence , and 78 insufficient evidence to recommend recommendations. The inclusion of separate scoping questions on treatments for complex presentations of PTSD was considered but decided against due to definitional issues and the virtual absence of studies specifically designed to clearly answer possible scoping questions in this area. Narrative reviews were undertaken and position papers prepared (one for adults and one for children and adolescents) to consider the current issues around CPTSD and make recommendations to facilitate further research. This paper describes the methodology and results of the ISTSS Guideline process and considers the interpretation and implementation of the recommendations.

The International Society for Traumatic Stress Studies New Guidelines for the Prevention and Treatment of Posttraumatic Stress Disorder: Methodology and Development Process