Pre- and perinatal conditions and processes may affect the risk for some forms of cancer in later life, while the insulin-like growth factor (IGF) system may play a role in both early somatic growth and later carcinogenesis. Birth weight and length, and the variation of major components of the IGF system immediately after birth, were analyzed in relation to selected physiological and pathological variables. The study comprised 331 healthy full-term newborns from whom blood samples were taken during routine phlebotomy no later than the fifth day of life. Measurements of IGF-I, IGF-II and IGF-binding protein-3 concentrations were performed. Birth length and weight were measured and information on socio-economic and medical variables was recorded. The concentrations of all three proteins were lower when blood bilirubin levels were high, possibly as a result of compromised liver function and/or as a component of an activated acute phase reaction. Birth weight was significantly higher by about 46 g among children whose IGF-I was higher by one SD, while the associations of birth weight and length with other components of the IGF system were in the predicted directions, albeit only in trend. We conclude that in early life, growth is related to the IGF system, mostly IGF-I. The latter is lower in children with jaundice, possibly because of hepatic dysfunction and/or as part of an acute phase reaction. We speculate that elevations of IGF-I in early life might explain the increased risk of cancer in individuals born with a higher birth weight.