Objective The insulin-like growth factor-1 (IGF-1) can protect damaged neurological system, but it is unknown whether exogenous IGF-1 can inhibit the productions of endogenous IGF-1 and IGF-1 receptor. This study aims to observe the changes of the expressions of IGF-1 and IGF-1 receptor mRNA in neonatal rats with hypoxic-ischemic brain damage (HIBD) and to explore the effects of IGF-1 treatment on endogenous IGF-1 and IGF-1 receptor. Methods Seven-day-old rats were subjected to unilateral carotid artery ligation and hypoxia exposure to establish a HIBD model. In situ hybridization was used to observe the changes of the expressions of IGF-1 and IGF-1 receptor mRNA in the injured regions of neonatal rats at differenft time points following HIBD. The expressions of endogenous IGF-1 and IGF-1 receptor mRNA between the HIBD group and the IGF-1-treated group at 12 hrs and 72 hrs following HIBD were compared by semi-quantitative analysis. Results The expressions of IGF-1 and IGF-1 receptor mRNA in the hippocampus began increasing at 48 hrs following HIBD, and reached a peak at 72 hrs. At 120 hrs post-damage, the expression of IGF-1 mRNA decreased to normal, while the expression of IGF-1 receptor mRNA maintained at a high level. In the cortex, the expressions of IGF-1 and IGF-1 receptor mRNA began increasing at 24 hrs post-damage, and decreased to normal at 96 hrs but their increased extent was less than that in the hippocampus. The expression of endogenous IGF-1 mRNA was not changed after IGF-1 treatment compared with the un-treated HIBD group. The expression of endogenous IGF-1 receptor mRNA remained unchanged 12 hrs after IGF-1 treatment, but significantly increased at 72 hrs. Conclusions IGF-1 and IGF-1 receptor mRNA in the cortex and the hippocampus increase after HIBD. Exogenous IGF-1 has no effect on the expression of endogenous IGF-1, but can up-regulate the expression of IGF-1 receptor.