All new parents in Sweden are invited to participate in parent groups by the Child Health Service (CHS), but not all choose to attend. The aim of this study was to identify factors that promote and impede the participation of parents in parent groups managed by the CHS during their child's first year. Twelve parents with children aged 10–12 months were interviewed during 2013. The interview text was analysed using qualitative manifest content analysis. The analysis resulted in eight categories. Those describing promoting factors were: feeling personally invited; having social hopes; being influenced by those around you; experiencing social fellowship; and being satisfied with the group leader. Categories describing impeding factors were: the parent group is not perceived to be addressed to both parents; the parents do not prioritise the group sessions offered; and expectations are not met. The study found that it is important for parents to feel personally invited and that the group leader's actions may be significant both for promoting and impeding participation in parent groups. The CHS nurse needs to be aware of parents' and children's individual needs and work actively to make all group participants feel included.