Objective: Obstructive sleep apnea syndrome (OSAS) in children is frequently associated with growth interruption. The objective of this study was to evaluate the effect of OSAS and adenotonsillectomy on the insulin-like growth factor-I (IGF-I) axis in children. Study design: Thirteen prepubertal children (mean age, 6.0 ± 2.8 years) were studied before and after adenotonsillectomy (T and A). Weight, height, overnight polysomnography, and IGF-I and IGF-binding protein-3 levels were evaluated before and 3 to 12 months after T and A. The children's weights and heights were monitored for 18 months. Results: The respiratory disturbance index improved from 7.8 ± 9.1 events/h to 1.0 ± 2.1 events/h after T and A (P < .02). Slow-wave sleep increased from 29.1% ± 7.2% to 34.6% ± 9.8% after T and A (P < .02). The weight standard deviation score increased from 0.86 ± 1 to 1.24 ± 0.9, 18 months after T and A (P < .01). Serum IGF-I levels increased from 146.3 ± 76.2 ng/mL before T and A to 210.3 ± 112.5 ng/mL after surgery (P < .01), but IGF-binding protein-3 levels did not change significantly. Conclusion: The respiratory improvement after T and A in children with OSAS is associated with a significant increase in serum IGF-I levels and weight. We conclude that the IGF-I axis is affected in children with OSAS.