Bisexual+ (e.g., bisexual, pansexual, queer) women experience higher rates of sexual violence (SV) and posttraumatic stress disorder (PTSD) than heterosexual and lesbian women, as well as unique identity‐related minority stress. We examined between‐ and within‐person associations between bisexual minority stress and PTSD symptoms related to SV in a sample of young bisexual+ women (N = 133) who reported adult SV (Mage = 22.0 years, range: 18–25 years; 85.0% White; 99.3% cisgender). We analyzed data from four waves of data collection (baseline to 3‐month follow‐up) using multilevel models. Controlling for SV severity, there was a significant within‐person effect of antibisexual stigma from lesbian/gay people on PTSD, β = .17, p = .010, suggesting that at waves when women experienced more stigma, they also reported higher PTSD symptom levels. At the between‐person level, women who reported higher levels of antibisexual stigma from heterosexual people, β = .26, p = .043, and anticipated binegativity, β = .29, p = .005, on average across study waves also reported higher average levels of PTSD. Additionally, anticipated binegativity explained the association between average antibisexual stigma and PTSD, β = .15, p = .014, 95% CI [0.45, 4.61]. Bisexual minority stress may be associated with higher PTSD symptom severity following SV among young bisexual+ women, and the anticipation of binegativity may be a target mechanism in this association. Study findings highlight the importance of examining the joint contributions of SV and minority stress to identify novel targets for future research and practice to address PTSD symptoms.