Insulin-like growth factors (IGF's) are mitogenic peptides bearing homology to proinsulin. IGF's are synthesized by many cell types in mammals and have been implicated as major factors controlling growth and differentiation during fetal life, infancy and childhood. Experimental evidence for these assertions is presented, using data from animal and human studies. The effects of IGF's on normal and abnormal growth processes are discussed, and specific examples are presented of disorders related to abnormal IGF production encountered in pediatric-age patients. Discussion is also included regarding the role of milk-borne IGF for the suckling. Lastly, future uses for IGF's are mentioned, with specific examples given for treating disorders, such as short stature and diabetes due to insulin resistance.