Objective: To examine the effects of cumulative victimization on intimate partner violence (IPV) victimization among young mothers. Method: With a cross-sectional design that utilized the life history calendar method and was grounded in developmental traumatology and life course stress theory, we interviewed 60 young mothers (ages 16 to 21) about their retrospective yearly experiences with community and school violence, witnessing IPV, physical maltreatment by a caregiver, and sexual victimization, beginning at age 5; we retrospectively assessed for annual IPV victimization beginning with 1st dating partner. We obtained an average of 15 years of data per participant, which we analyzed using multilevel modeling. Results: This high-risk sample reported much higher rates of victimization than did similarly aged national samples, with lifetime prevalence of each type ranging from 60% to 84%. Cumulative victimization during childhood was positively associated with cumulative victimization during adolescence. A higher rate of cumulative victimization during childhood was associated with a steeper increase in the rate of IPV victimization during adolescence, after controlling for a range of predictors, though childhood cumulative victimization was not linked to IPV at age 16. Conclusions: Consistent with developmental traumatology and life course stress theory, which emphasize the role of early and proliferating stressors in shaping poor outcomes, childhood experiences with cumulative victimization may increase young mothers’ vulnerability to IPV victimization during adolescence. Researchers should embrace innovative methods to explore developmental trajectories of cumulative victimization, especially among high-risk groups; clinical practice and dating violence interventions must be evidence-based and trauma-informed to be effective. (PsycINFO Database Record (c) 2017 APA, all rights reserved)