Objective: This paper assesses the role of family cohesion in therelationship between polygamy and mental health and whether this varies as afunction of the father’s involvement. Background: Studies show that polygamyhas a detrimental effect on children’s mental health, yet familial variablesthat may account for this relationship have rarely been explored. Familycohesion is crucial for the relationship between a range of familial riskfactors and mental health. Method: Data about family structure, familycohesion, mental health, father involvement, and other relatedsociodemographic variables were collected from students from randomlyselected middle schools (students N = 758) in Jeddah, Saudi Arabia. Results:Polygamous marital structure predicted more psychosocial problems and higherinternalizing symptoms, but not externalizing problems. Polygamy had anindirect association with psychosocial problems through family cohesion, andfather involvement moderated the relationship between polygamy and familycohesion. Conclusion: The findings suggest that living in polygamous familiesmay impair the mental health of middle school–aged children, in part bydiminishing family cohesion. Additionally, low father involvement mayexaggerate threats to family cohesion resulting from polygamy and subsequentchild mental health consequences. However, contrary to previous research,children’s externalizing behavior did not vary by polygamous maritalstructure. Implications: Family‐focused therapies, which include the fathers,may be of particular use to support this at‐risk group