Background Preterm-born children are at increased risk of adverse developmental outcomes, and their parents may experience increased stress levels. The Mother–Infant Transaction Program (MITP) is an early intervention that aims to enhance the parent–infant relationship and child development. The present study investigated differences in parents’ experience of stress and concerns about caring for their preterm-born child according to whether they participated in the programme. Parental satisfaction with the intervention was also explored. Methods As part of a follow-up study at 36 months, a randomized controlled trial of the MITP—14 parents of 11 children from the intervention group, and 17 parents of 14 children from the control group were interviewed by the use of semi-structured focus group interviews. The interviews were analysed thematically. Results The intervention parents reported that the knowledge, advice, guidance and emotional support given during the intervention made them feel less stressed and more confident, competent and secure caring for their preterm born child than they would otherwise have been. The control parents described feeling less involved and emotionally supported, and seemed more anxious about their child’s development than the intervention parents. All parents were vigilant and alert to their child’s needs and monitored developmental milestones carefully. Conclusion This qualitative exploration of the influences of the MITP revealed a positive impact of the intervention and seems to be an important educational and supportive initiative. Thus, reducing parental stress and enhancing confidence in the parental role.