Anticipated Impact on Veteran's Healthcare: PTSD is a critical obstacle to the recovery of Veterans with serious mental illness (SMI; psychotic spectrum and bipolar disorders). The Veterans Health Administration (VHA) has made treatment of PTSD a high priority and has initiated dissemination of evidence-based practices (EBPs) for PTSD across the national VHA system. However, EBPs for PTSD have not been tested among, and are largely not provided to Veterans living with both PTSD and SMI, despite high co-occurrence rates and profound associated negative functional impact. This study will: [Aim 1) administer the Cultural Formulation Interview (CFI) during a pre-pilot study of WET with 10 Veterans with SMI and PTSD to inform how best to incorporate aspects of cultural identity into the WET intervention pilot-testing in Aim 2; Aim 2) conduct a pilot randomized controlled trial (RCT) with 48 Veterans with SMI and PTSD to examine the feasibility and acceptability of WET, [monitor fidelity], and preliminarily evaluate clinical and functional outcomes; Aim 3) complete a well-specified process evaluation to determine what, if any, considerations are needed to optimize WET for Veterans with SMI and regarding culturally responsive methods. Overall impact will be to move WET towards full evaluation as a potential EBP for Veterans with PTSD and SMI. Project Background: PTSD is prevalent among Veterans and others with SMI,3-8contributing to substantial mental and physical health impairments.7,14-22 Written Exposure Therapy (WET) is a new EBP for PTSD that may have special clinical utility for Veterans with SMI and PTSD. 31,41-42,44 However, such Veterans have been largely excluded from PTSD clinical trials, and no WET trials to date have focused on an SMI population.42,45 Further, there are significant race and ethnicity disparities in PTSD and SMI prevalence and treatment, even in VHA.2,47 For instance, persistence and chronicity of SMI and PTSD are higher for Black, Indigenous, and other people of color (BIPOC),48,103 underlining the need for PTSD EBPs to be delivered in culturally responsive ways. Project Objectives: The proposed CDA-2 research will address research and clinical gaps by integrating culturally responsive assessment methods and testing the feasibility and acceptability of WET among Veterans with SMI and PTSD. [The first step of this research will focus on administering culturally responsive assessments and WET to Veterans with PTSD and SMI in a training trial (n = 10), including qualitative interviews exploring participants' experiences with and views of these instruments and WET.] The second step will involve completing a small randomized controlled trial of WET to examine feasibility, acceptability, and fidelity of WET, and to preliminary explore changes to clinical outcomes and functioning among 48 Veterans randomized to WET (n = 32) vs. a PTSD psychoeducation control intervention (n = 16). We will assess rates of recruitment, initial inter...