This study investigated sex-specific predictors of violent and nonviolent mate guarding used by men (n=399) and women (n=951) in heterosexual relationships, using both self-reports and reports on partners. We found, contrary to some previous evolutionary assumptions, that men and women showed similar degrees of controlling behavior, and that this predicted physical aggression to partners in both sexes. We also predicted from evolutionarily based studies that men's and women's control and aggression would vary as a function of female fecundity and mate value (relative to peer group and to partner). Fecundity was associated with men's and women's controlling behavior, but not their physical aggression: relationships where the woman was fecund showed higher rates of control. According to partners' reports, men and women who had lower mate values showed more controlling behavior and (to a lesser extent) more physical aggression. There was no support for the prediction that higher mate-value partners would be guarded more than lower mate-value ones. The following limitations are discussed: the sample and method of data collection, and the lack of information on the women's hormonal status.