Background: Primary goal of growth hormone (GH) treatment for short children is to achieve an adult height in the normal range. Different GH treatment strategies to achieve this goal include titration of GH dose according to serum insulin-like growth factor I (IGF-I) concentrations. However, IGF-I levels do not always correlate well with the growth response. The purpose of this study is to identify the factors affecting IGF-I concentration in each disease and to correct the related factors and then to identify the relationship between IGF-1 and treatment response. Methods: In this study, data of pre-pubertal children with idiopathic growth hormone deficiency (IGHD), organic GHD (OGHD), Turner syndrome (TS), small for gestational age (SGA) who were treated with recombinant human GH more than one year were obtained from the LGS Database. The LGS has been progressing since 2012 and is an open-label, multicenter, prospective, and retrospective observational study. Results: Among 2,021 registered in LGS, the subjects were 366 except for the violation of selection criteria. Among them, IGHD was 252, 16 OGHD, 31 TS, and 67 SGA. The mean age of IGHD was 6.02, and the mean bone age was 4.49 years. OGHD was 7.38, 5.74, TS was 7.13, 6.52, and SGA was 5.61, 4.96 years. The height SDS according to chronologic age was -2.76 in IGHD group, OGHD -2.33, TS -2.9, SGA -2.57. In the IGHD and SGA group, IGF-I level has a positive correlation with weight and BMI (weight; r=0.0071 in IGHD, r=0.0009 in SGA, BMI; r=0.0411 in IGHD, r=0.003 in SGA). IGF-I showed a negative correlation with chronological age in the IGHD group (r=0.0411) and mid-parental height in the SGA group (r=0.0069). There was no significant relationship between pretreatment IGF-I level and growth response. However, in the IGHD group, the growth response was significantly higher when the change in IGF-I SDS value was 1 or more (P=0.0013). Conclusion: This study is the first study using LGS data to identify factors affecting IGF-I levels in Korean children with short stature and the relationship with treatment response. IGF-I levels were positively correlated with body weight in IGHD and SGA groups. There was no significant relationship between pre-treatment IGF-I levels and post-treatment growth response. In conclusion, IGF-I concentrations should be used as a tool for treatment compliance rather than for efficacy determination.