Background: Functions of a family refer to its systematic characteristics and include the ability of families to protect the principles governing this institution to keep its wholeness. The aim of this study was to compare the performance of families with mentally retarded children and families with healthy children.

Methods: This case-control study was conducted in 2015 in Ahvaz City, Iran. The population consisted of 86 families with mentally retarded children and 86 families with normal children living in Ahvaz. Data were collected by demographic and family functioning (FAD) questionnaire and then analyzed by t-test and Mann-Whitney test through SPSS ₂₁ software.

Results: The findings showed no significant difference between the 2 groups in family performance and total performance.

Conclusion: Although no significant difference was observed in the performance of families with and without mentally retarded children, poor performance of these families in different parts of questionnaire showed that  developing support mechanisms can be useful.