Although common practice in Veterans Affairs (VA) PTSD clinics, it is unclear whether preparatory treatment improves trauma-focused treatment (TFT) completion and outcomes. Furthermore, little is known about whether treatment-seeking veterans in naturalistic settings would chose to prioritize preparatory treatment if given the option of a phase-based approach or direct access to TFT, and how substance-related problems (SRPs) influence this treatment choice. The first aim of this study was to explore how co-occurring SRPs (ranging from none to moderate/severe) influence PTSD treatment choices in a naturalistic setting where veterans were offered a choice between a phase-based approach (i.e., preparatory treatment) or direct access to TFT. The study also examined whether initial treatment choice and severity of co-occurring SRPs influenced TFT completion and outcomes. The second aim was to investigate whether preparatory treatment led to superior TFT completion or outcomes, irrespective of co-occurring SRPs. Analyses were conducted using archival data from 737 United States veterans referred for outpatient VA PTSD treatment. SRPs did not predict initial treatment choice or the length of preparatory group participation. Neither SRPs nor preparatory group participation predicted TFT completion or outcomes (measured as change in PTSD and depression symptoms from pre- to post-TFT). Preparatory group participation did not predict improved TFT completion or outcomes, irrespective of co-occurring SRPs. These findings suggest that veterans with PTSD symptoms and co-occurring SRPs may make similar treatment choices and benefit from either a phase-based approach or direct TFT initiation, and preparatory treatments may not increase patient readiness for veterans seeking TFT. (PsycInfo Database Record (c) 2020 APA, all rights reserved).