Premature dropout from posttraumatic stress disorder treatment (PTSD) hinders treatment response. Studies have primarily used quantitative methodology to identify factors that contribute to Veterans' premature dropout, which has yielded mixed results. Qualitative methods provide rich data and generate additional hypotheses about why Veterans discontinue PTSD treatment. This study aimed to understand Veterans' reasons for dropping out of prolonged exposure therapy (PE) and to examine if there are differences in reasons for dropout between three delivery modalities: in-home, in-person (IHIP), office-based telehealth (OBT), or home-based telehealth (HBT). Twenty-two Veterans who dropped out of PE from a parent randomized clinical trial participated in individual qualitative interviews about potential contextual and individual factors related to discontinuation. Team-based coding was used to conduct open and focused coding. Themes were generated that described factors that influenced Veterans' dropout from PE and constant comparison was used to explore differences in reasons between the three modalities. Most Veterans had multiple reasons for dropping out and reasons were similar across delivery modalities with few differences. Practical barriers (e.g., scheduling difficulties), attitudes toward mental health providers and therapy (e.g., stigma), psychological and physical health factors (e.g., perceived worsening of symptoms, pain), and the therapeutic context (e.g., disliking aspects of PE) contributed to Veterans' decisions to drop out from PE. Veterans in OBT reported more types of practical barriers than Veterans in HBT and IHIP. These findings can help generate hypotheses about interventions that may promote engagement and future studies should continue to study how to reduce dropout. (PsycInfo Database Record (c) 2023 APA, all rights reserved).