Parents attempt to influence their children’s mating decisions in order to get sons- and daughters-in-law who comply with their preferences. One trait that parents consider important in a prospective in-law is similarity in the family background. This paper attempts to identify the dimensions of similarity in a prospective son- and daughter-in-law’s family that are of interest to parents, and to test several hypotheses. More specifically, it is hypothesized that parents ascribe more importance on certain family similarity dimensions and less importance on others, while it is also hypothesized that in-law preferences for similarity are independent of the parents’ and of the prospective in-law’s sex. In Study 1, using semi structured interviews, nine dimensions of family similarity are identified that are of interest to parents. By using principal components analysis, in Study 2, these traits are classified into two main preference categories. Through further statistical analysis, it is found that some dimensions are preferred over others, while the parents’ and the prospective in-law’s sex do not predict how much weight parents place on family similarity dimensions. The implications of these findings are further discussed.