This study examined whether maternal warmth in early childhood moderates the association between preterm birth and problems in peer relationships and low engagement in romantic relationships in adolescence. We studied 9193 individuals from the Millennium Cohort Study in the United Kingdom, 99 (1.1%) of whom were born very preterm (VPT; < 32 weeks of gestation) and 629 (6.8%) moderate-to-late preterm (MLPT; 32–36 weeks gestation). Maternal warmth was reported by the mothers when their children were 3 years old. Peer relationship problems were reported by both the participants and their mothers at 14 and 17 years. Further, participants reported their engagement in romantic relationships at 14 and 17 years. All outcome variables were z-standardized, and the moderation effect was examined via hierarchical linear regressions. Compared to full-term birth, both MLPT and VPT birth were associated with lower engagement in romantic relationships at 17 years of age (b =.04, p =.02; b =.11, p =.02, respectively), and VPT birth was associated with increased peer relationship problems at 14 (b =.29, p =.01) and 17 years of age (b =.22, p =.046). Maternal warmth in early childhood was similarly associated with lower peer relationship problems in MLPT, VPT and full-term born adolescents. However, there was no influence of maternal warmth on engagement in romantic relationships at 17 years of age. There is no major modifying effect of maternal warmth in early childhood on the association between PT birth and peer relationship problems and low engagement in romantic relationships at 14 and 17 years of ages.