Objective: Preterm birth has been associated with altered body composition, especially increased fat mass (FM) and decreased bone mineralization, and leptin and IGF-1 have been suggested to be involved in the regulation of both. We aimed to study the interplay between leptin, IGF-1, FM and bone mineralization measured in infancy and childhood of children born preterm. Design: Observational study. Patients/subjects: Seventy-nine (40 boys) preterm-born children (gestational age ≤32 weeks and/or birth weight ≤1500 g) aged 8 years. Measurements: Serum leptin and IGF-1 were measured at term age, at 3- and 6-month corrected age (CA), and 8 years. Body composition (fat and lean mass) and bone parameters (bone area, mineral content and density) were measured by Dual-energy X-ray Absorptiometry (DXA) at term age, 6-month CA and 8 years. Results: Leptin was positively associated with FM at all time points and with bone parameters at term age and 6-month CA. IGF-1 was associated with body composition and bone density at most of the time points. Explained variation in bone mineralization increased significantly by adding bone area (BA) and height to the models. Conclusions: During infancy and childhood, leptin and IGF-1 were associated with body composition in preterm-born children. In addition, leptin was associated with bone parameters in early infancy, but not in childhood. It is hypothesized that a complicated interplay between multiple pathways, which most likely changes over time, is involved in regulation of body composition and bone mineralization of preterm-born infants.