BACKGROUND: Earlier research has shown that the care of families expecting a malformed child should be intensified and that the topic is understudied. AIM: This study aimed at generating a practical nursing theory of interaction between caregivers and families expecting a malformed child, as experienced by families. METHODS: A grounded theory study was undertaken at a university hospital, Finland. Data consisted of semi-structured interviews with 29 mothers and fathers, analysed using the constant comparative method. FINDINGS: The interaction process starts with the confirmation of the diagnosis. It usually comes as a shock to the parents, and gives rise to questions about the nature of the malformation, family members’ relationship with themselves, family relationships and relationships with people outside the family. These questions are crucial to the family’s coping and form the core of interaction. Families’ own coping strategies are either reinforced or undermined by caregivers’ actions and are reflected in parents’ expectations about caregivers, which in part account for their actions and experiences of interaction. The care system as an interactive environment is part of a process which results in the experiences of being helped or being left without help. The core of the interaction process comprises two dimensions: gaining strength and losing strength in relation to malformation issues. CONCLUSIONS: The findings of the study are consistent with earlier research and complement it by providing a detailed delineation of the interaction from the perspective of the family. They can be used to formulate recommendations for improving caregivers’ interactive skills and awareness of the topic through training. The care system should be developed to ensure that families receive psychological support and that the family as a whole receives proper care. Consideration of the viewpoint of siblings is a challenge for further research.