This study examined the validity of the Interpersonal Exchange Model of Sexual Satisfaction (IEMSS) in long-term, heterosexual sexual relationships. The IEMSS proposes that sexual satisfaction depends on one's levels of rewards and costs in the sexual relationship, one's comparison levels (CL) for rewards/costs, and one's perceptions of the dyadic equality (EQ) of these rewards/costs. Sexual satisfaction is expected to be greater to the extent that, over time, levels of rewards (REW) exceed levels of costs (CST), relative reward levels (CLREW) exceed relative cost levels (CLcst), and interpersonal equality of rewards (EQrew) and of costs (EQCST) is perceived to exist. Married/cohabiting community volunteers and university alumni/staff completed two questionnaires, 3 months apart. The results obtained from this well-educated, relationally satisfied sample (N= 143) provided excellent support for the IEMSS. Hierarchical regression analysis revealed that each component of the model (REW - CST, CLrew - CLcst, and EQrew, EQcst) added to the prediction of sexual satisfaction as expected, accounting for 75% of the variance. Repeated measurement of the IEMSS components offered a better prediction of sexual satisfaction than a one-time measure alone. Neither gender nor relationship satisfaction interacted with the IEMSS components. However, including relationship satisfaction (but not gender) in the model significantly improved the prediction of sexual satisfaction. It was concluded that the model should be revised to include relationship satisfaction. Both the exchange components of the IEMSS and sexual satisfaction uniquely predicted relationship satisfaction. The IEMSS offers a promising approach for understanding sexual satisfaction and its relationship to relationship satisfaction, as well as for reconciling inconsistent findings in the literature.