Sexual risk taking may be heightened among U.S. service members and veterans reporting military sexual assault (MSA) exposure. MSA increases the risk for posttraumatic stress disorder (PTSD), which is a common correlate of sexual risk taking among civilians. PTSD may relate to sexual risk taking through its association with alcohol use, which increases impulsivity and risky behavioral engagement. Male survivors may be at notably higher risk given greater overall alcohol use and engagement in sexual risk taking relative to female survivors. This study assessed whether higher alcohol use mediated the association between PTSD and sexual risk taking among MSA survivors, and whether this effect differed by sex. Participants included 200 male and 200 female service members and veterans (age: M = 35.89, SD = 5.56) who completed measures of PTSD symptoms, alcohol use, sexual risk taking, and a demographic inventory. In a moderated mediation analysis using linear regression, higher PTSD severity was associated with higher alcohol use, and higher alcohol use was associated with higher sexual risk taking. A significant indirect effect of alcohol use was observed, which was stronger among men. To reduce sexual risk taking among MSA survivors, it may be beneficial to target PTSD symptoms and alcohol use with sex-specific interventions. This line of inquiry would be strengthened by longitudinal studies that explore the fluidity of these experiences to identify periods of elevated risk. Studies that examine alcohol use expectancies and sexual delay discounting could expand our understanding of these associations.