This study is intended to determine whether twice daily weight based dosing with recombinant human insulin-like growth factor (rhIGF-1) will safely and effectively increase the growth of prepubertal children with short stature associated with low IGF-1 levels but who produce sufficient growth hormone (GH). Subjects will be randomized to either an observation arm or to active treatment.

Prepubertal growth failure associated with primary IGF-1 deficiency (IGFD). Primary IGFD is a term that has been used to describe patients with intrinsic cellular defects in GH action. In this protocol, primary IGFD is defined as short stature (height standard deviation score\[SDS\]\<-2 below the mean for age and gender), low serum IGF-1 (IGF-1 SDS \<-2 below the mean for age and gender), and levels of growth hormone (GH) that are normal (≥7ng/mL) after a GH stimulation test. Primary IGFD is believed to result from a lower than normal ability to produce IGF-1 when exposed to normal levels of GH, i.e., a type of GH insensitivity or GH resistance. This trial is one year, randomized, open label, observation-controlled, parallel-dose comparison efficacy and safety study conducted in approximately 40 centers across the United States.