<i>Objectives:</i> To describe glucose metabolism changes during growth hormone (GH) treatment in juvenile idiopathic arthritis (JIA). <i>Study Design:</i> Observational study in 58 children on glucocorticoid therapy (GC) for JIA, of whom 28 received late GH therapy (7.3 ± 3.4 years into GC), 15 early GH therapy (1.2 ± 0.1 years into GC), and 15 no GH therapy. The GH dose was 0.46 mg/kg/week. Oral glucose tolerance testing with insulin and glycosylated hemoglobin assays were performed yearly. Nonparametric tests were used to compare groups after 3 years and regression analyses to estimate factors predicting glucose AUC and HOMA-IR at baseline and after 3 years. <i>Results:</i> GH combined with GC was associated with an increase in mean fasting insulinemia. Late GH therapy patients exhibited significant increases over time in mean fasting glycemia (p = 0.01), mean 2-hour postglucose load glycemia (p < 0.05), mean AUC for glucose (p < 0.05), and mean HOMA-IR (p < 0.05). Impaired glucose tolerance was found in 16/43 GH-treated patients (37%) and transient diabetes in 2 (5%) patients. <i>Conclusions:</i> GH treatment in JIA children decreased insulin sensitivity but had only modest effects on glucose tolerance. Close monitoring by oral glucose tolerance testing is crucial before and during GH treatment, particularly during puberty and relapses.