Introduction: The relationship between maladaptive perfectionism and Internalizing (ID) and Externalizing Disorders (ED) in children needs to be better understood, along with the intergenerational transmission of these traits from parents to children. The present work aimed to share light on both these issues. Method: 39 children with ID, 19 with ED, and their parents were recruited*. The Multidimensional Perfectionism Scale, the Big Five Inventory, the Child and Adolescent Perfectionism Scale, and the Hierarchical Personality Inventory for Children were used. The association between parent personality and perfectionism traits and children’s perfectionism dimensions was evaluated through hierarchical regression analysis. Results: ID and ED groups did not differ significantly concerning perfectionism. Fathers presented higher scores than mothers in Self-Oriented Perfectionism, Other-Oriented Perfectionism, and Socially-Prescribed Perfectionism. Parents of children with ID report higher levels of Obedience in their children, while parents of children with ED reported higher levels of Creativity and Perseverance. Significant associations were found between perfectionism in parents and their children, as well as between perfectionism and the personality of children. Conclusion: Results suggest a transdiagnostic nature of Perfectionism and support the transgenerational transmission of the personality traits investigated.