Posttraumatic nightmares (PTNs) are common among service members with a history of combat or mission-related trauma and are associated with decreased well-being. Unfortunately, beyond establishing an association between mental health symptoms and PTNs, the existing literature fails to provide a more comprehensive understanding of factors associated with PTNs. The effectiveness of current recommended treatments is frequently debated, with the literature varying in levels of support. Treatment of PTN is complicated, given their association with a number of mental health difficulties including posttraumatic stress disorder (PTSD), anxiety, and depression. The present study sought to better delineate the association of these difficulties with PTNs, in an effort to inform and improve treatments for the nation's service members. This study utilized de-identified data collected during standard procedures for an interdisciplinary intensive outpatient program for service members with a history of traumatic brain injury and/or psychological health conditions (N = 1,550). Study analyses were performed under a Walter Reed National Military Medical Center institutional review board-approved protocol. Three cross-sectional forward likelihood ratio logistic regressions predicting the presence of PTNs were conducted while controlling for the alpha-blocker prazosin, as it is recommended for the treatment of PTSD-associated nightmares. Separate models were created for posttraumatic stress symptoms (PTSS), depression, and anxiety because of multicollinearity concerns. Additional variables considered for inclusion were psychological symptoms (e.g., suicide ideation, postconcussive symptoms), satisfaction with life, sleep (e.g., pain that disrupts sleep, early awakenings, sleepiness), demographics (e.g., sex, race/ethnicity, marital status, age), and military characteristics (e.g., rank, branch, special operator status, time in service). PTSS (odds ratio [OR]: 1.13), anxiety (OR: 1.19), and depression (OR: 1.19) were associated with increased odds of PTNs when controlling for prazosin. Each of the final models accounted for a significant amount of variance in the presence/absence of PTN. The included variables differed across models. The PTSS model included pain that disrupted sleep, postconcussive symptoms, special operator status, and early awakenings. The anxiety model included postconcussive symptoms, pain that disrupted sleep, special operator status, and prazosin use. The depression model included postconcussive symptoms, pain that disrupted sleep, special operator status, difficulty falling asleep within 30 min, and prazosin use. Although most variables were associated with an increased odds of PTNs, postconcussive symptoms in the PTSS model and special operator status in all 3 models were associated with decreased odds of PTNs. These findings are illustrated in Tables2 to 4. Findings support the association of PTSS, anxiety, and depression to PTNs, and, importantly, suggest that other factors may be equally or more important in understanding PTNs. Notably, increased odds of PTNs were observed among patients with pain that disrupts their sleep. The cross-sectional nature of the study allows examination of these co-occurring symptoms as they would present in the clinic, potentially informing assessment and treatment strategies; however, it precludes consideration of temporal relationships. Results highlight the importance of considering comorbid symptoms and relevant military characteristics to gain a more complete understanding of PTNs. Future research utilizing longitudinal methods are needed to inform the temporal/causal aspects of these relationships.