We investigated the effect of improving glycemie control on serum concentrations of insulin-like growth factors I and II (IGF-I and IGF-II). In 22 adults followed during an intensive home glucose monitoring program for 6 mo, no effect of improving control was seen on either IGF-I or IGF-II. Similar results were obtained in young diabetic children <10 yr of age and in diabetic adolescents with detectable puberty before entering the study. In older diabetic children without evidence of puberty before treatment (Tanner prepubertal stage 1), initial IGF-I concentrations were low, but increased during establishment of glycemie control. Puberty developed during therapy in this latter group. Our data do not support a “global” effect of glycemie control on serum IGF-I in diabetic patients. Increases of IGF-I with better glycemie control appear most likely to occur when the metabolic consequences of diabetes have suppressed normal pubertal increases of IGF-I. IGF-II concentrations were unaffected by glycemie control in all subjects.