【Background】This article provides a description of the rationale, design, and methods of a multisite clinical trial which evaluates the potential benefits of an evidence-based psychosocial treatment, STAIR Narrative Therapy, among women with posttraumatic stress disorder (PTSD) related to interpersonal violence who are seeking services in public sector community mental health clinics. This is the first large multisite trial of an evidence-based treatment for PTSD provided in the context of community settings that are dedicated to the treatment of poverty-level patient populations.【Methods】The study is enrolling 352 participants in a minimum of 4 community clinics. Participants are randomized into either STAIR Narrative Therapy or Treatment As Usual (TAU). Primary outcomes are PTSD, emotion management and interpersonal problems. The study will allow a flexible application of the protocol determined by patient need and preferences. Secondary analyses will assess the relationship of outcomes to different patterns of treatment implementation for different levels of baseline symptom severity.【Discussion】The article discusses the rationale and study issues related to the use of a flexible delivery of a protocol treatment and of the selection of treatment as it is actually practiced in the community as the comparator.【Trial registration】Clinicaltrials.gov identifier: NCT01488539.