The observation that aggression between intimate partners runs in families is typically explained from a social learning perspective that contends children learn aggression against intimate partners by being exposed to this type of violence in their environment. This explanation considers environmental influences on behavior without taking into account possible genetic factors that could be asserting an influence on behavior. The current study explored the extent to which genetic and environmental factors contributed to individual differences in the expression of intimate partner aggression by assessing 134 monozygotic and 41 dizygotic pairs of same-sex twins recruited through advertisements. Participants completed self-report questionnaires measuring physical and psychological aggression within relationships. Results of statistical analyses indicated that genetic factors explained the family similarities in psychological and physical aggression against intimate partners. Further analysis revealed that most of the genetic influences contributing to the receipt of aggression were also responsible for the use of aggression within relationships, suggesting a genetic predisposition to becoming involved in aggressive relationships. Although the results refute the social learning perspective on the familial similarities in intimate aggression, they are consistent with behavioral genetic studies of general aggression. Future research should attempt to replicate these findings with a larger, more diverse sample. Tables, figures, references