The concentration of IGF-I in blood of young pigs has previously been found to be genetically associated with feed efficiency and performance in pigs. To test these associations, data from the ISU selection line for residual feed intake (RFI) were used. Compared to controls, in the line selected for increased efficiency through reduced RFI, a correlated response in the expected downwards direction was observed for juvenile IGF-I. Genetic correlations of IGF-I were 0.63 with RFI and 0.78 with feed conversion ratio. These results confirm that juvenile IGF-I is a good physiological indicator of genetic merit for economically important efficiency traits, particularly since it is measured early in an animal’s life.