Mothers and fathers within families are assumed to exert mutual influences on each other (i.e., to be interdependent). However, there is little evidence on the nature of this interdependence. Mother-Father interdependence was examined in a middle-class, White nonclinic sample in Sydney, New South Wales, Australia, consisting of intact families with an early school-age child. Interdependence was investigated in the forms of correlation, similarity, and complementarity for variables in 4 domains of parenting. For individual variables there was a substantial degree of similarity. However, there was considerable diversity and complexity in the pattern of similarity and difference, across variables and for different families. Interdependence appears to take various forms in different families. Better marital quality and greater similarity of personality were not related to more mother-father similarity. Explanations for similarity are considered.