Individuals with posttraumatic stress disorder (PTSD) are at an increased risk of being classified as overweight or with obesity in part due to PTSD symptoms (e.g., sleep disturbance and social isolation) interfering with activity and healthy eating. MOVE!+UP is a 16-week behavioral weight management program, tailored to address such barriers for people with PTSD, by combining evidence-based weight loss education and support with cognitive behavior therapy skills to reduce PTSD symptom-based weight management barriers. This qualitative study examined veterans' (n = 37) perceptions of social support relevant to weight management, health behaviors, and mental health while participating in an uncontrolled pilot of MOVE!+UP. Template analysis of transcripts from 1-hr semistructured qualitative interviews identified four main categories of participant responses. Participants described positive aspects, particularly cohesiveness around a shared veteran identity, feeling less alone, accountability, and having others eat healthier and exercise with them. Conversely, relationship-based barriers included other participants' poor MOVE!+UP group session attendance and engagement, and loved ones' encouragement of making unhealthy choices. Many described having limited relationships or trouble accessing available support. Finally, PTSD symptoms were a significant barrier to utilizing social support to facilitate weight loss. Findings suggest future behavioral weight management programs should recruit members with similar backgrounds to capitalize on shared experience, encourage consistent attendance and meaningful participation, deliver education about how to leverage social support from others outside the program, and address mental health symptoms that impede social support and healthy lifestyles. (PsycInfo Database Record (c) 2022 APA, all rights reserved).