This research tested the hypothesis that marital satisfaction is a psychological state regulated by evolved mechanisms that monitor spousal cost-infliction and benefits. Three separate data sources were used to study a sample of married couples. First, 214 participants provided information on their personality and marital satisfaction. Second, participants provided information on their spouse's personality, mate guarding and susceptibility to infidelity. Third, couples were interviewed by two interviewers, who subsequently provided independent ratings of each participant's personality. Results indicate that costs associated with spouse's personality, mate guarding and susceptibility to infidelity negatively correlate with participants' marital satisfaction. Discussion evaluates the utility of an evolutionary perspective on marital satisfaction and spousal cost-infliction.