Consistent with previous studies, psychological and physical aggression were significantly correlated in the current study. In addition, there was considerable overlap between the factors that influenced both. For both, the use and receipt of aggression, the high genetic correlations between psychological and physical aggression suggests that they are influenced by essentially the same genetic factors. However, the non-shared environmental factors that influence each seem to have some independence as indicated by the low non-shared environmental correlations between psychological and physical aggression. Therefore, it seems that there are both etiologic similarities and independence in the factors that influence psychological and physical aggression. An interpretation of the results could be that there may be a modest genetic predisposition towards aggressive behavior, but what determines whether someone is physically versus psychologically aggressive is primarily due to environmental experiences. Previous studies that have investigated the link between the use of physical and psychological aggression in intimate relationships consistently show that the two are highly intercorrelated. This study first explored the extent to which physical and psychological aggressions were associated. Then, using multivariate behavior genetic methods, it investigated the extent to which this association was due to common genetic and/or environmental influences. Participants of the study consisted of 185 pairs of same-sex twins, who had experience in an adult intimate relationship. Tables, figures, references