According to Toman, the success of a marriage depends partly on the fortunate matching of husband and wife according to the rank of each among childhood siblings. An example of this would be if the husband were an older brother of a sister, and the wife the younger sister of a brother. Neither will tend to have a rank conflict, nor a conflict over accepting the other sex. An unfavorable match would be the marriage of an older brother of a brother to an older sister of a sister. The author discusses various such configurations in detail and illustrates his thesis with a clinical example.