Aim: To examine the differential effects of an early intervention programme for infants born preterm on neurodevelopment and parental mental health according to family social risk. Method: One hundred and twenty infants born earlier than 30 weeks' gestation were randomized to early intervention (n=61) or control groups (n=59). Cognitive, language, and motor outcomes were assessed by blinded assessors at 2 years, 4 years, and 8 years, and primary caregivers completed questionnaires on their anxiety and depression. Outcomes at each time point were compared between groups using linear regression with an interaction term for social risk (higher/lower). Results: There was evidence of interactions between intervention group and social risk for cognition at 2 years and 4 years, motor function at 4 years, and language at 8 years, with a greater intervention effect in children from higher social risk environments. In contrast, the impact of early intervention on parental depressive symptoms was greater for parents of lower social risk than for those of higher social risk. Interpretation: Effects of early intervention on outcomes for children born preterm and their caregivers varied according to family social risk. Family social risk should be considered when implementing early intervention programmes for children born preterm and their families. What this paper adds: Intervention is associated with better early cognitive functioning for children in higher social risk families. Positive effects of intervention for the high risk group were not sustained at school-age. Intervention has a greater effect on primary caregiver mental health in the lower social risk group compared with higher social risk.