Despite the pervasiveness of adult sexual assault (ASA), evidence-based knowledge on the risk factors for sexual victimization is insufficient. Here, we investigated the etiology of ASA in a population-based Finnish twin sample. Specifically, we estimated the extent of the genetic and environmental influences on the risk of ASA, and we examined its phenotypic and genetic associations with five types of child maltreatment (CM). We found large unique environmental, but also small genetic influences on the risk of ASA, motivating further research on situational and behavioral conditions potentially exploited by sexually motivated perpetrators. The pre- valence of ASA was highest among victims of severe child sexual abuse. However, when accounting for the co-occurrence of multiple types of CM, emotional abuse was the strongest predictor of ASA. We further examined, and could not entirely rule out, the possibility of common genetic and environmental pathways underlying CM and ASA. Lastly, we focused on sex differences. Emotional and physical abuse were the strongest predictors of ASA in women and men, respectively, and genetic influences on the risk of ASA were larger in women than men. However, such higher heritability did not reflect sex-limited genetic effects, but, rather, women’s systematic exposure to environmental risk of ASA.