Circulating levels of insulin-like growth factor-I (IGF-I) and its principal binding protein IGFBP-3 are reduced, whereas those of the inhibitory binding protein, IGFBP-1, tend to be high in children and adolescents with type 1 diabetes mellitus (T1DM). These abnormalities are thought to arise because of relative portal hypoinsulinaemia and partial resistance at the hepatic growth hormone (GH) receptor. During adolescence, reductions in IGF-I and IGF bioactivity lead to feedback for GH hypersecretion and the elevated GH and low IGF-I levels lead to an increase of the normal insulin resistance encountered during puberty. Low IGF-I levels, but in particular elevated GH levels, have been implicated in the pathogenesis of diabetic microangiopathic complications, in particular, renal hypertrophy, glomerular hyperfiltration and the development of microalbuminuria. Early study of IGF-I replacement with recombinant human IGF-I (rhIGF-I) demonstrated, in the short term, reductions in GH hypersecretion with improved insulin sensitivity and, in the longer term, reductions in insulin requirements and improvements in HbA1c levels. However, larger doses of rhIGF-I were associated with retinopathy either due to rapid improvements in glycaemic control or direct effects of high levels of 'free' IGF-I. More recently, pilot studies using the combination of rhIGF-I/rhIGFBP-3 have confirmed the physiological efficacy of IGF-I replacement in T1DM. The combined treatment is better tolerated and may result in reduced tissue exposure to high levels of 'free' IGF-I. Longer term clinical studies with this IGF-I/IGFBP-3 combination are needed.