We report here the acute and long-term influences of deltamethrin on the expression of IGF-I, IGF-II and GH-I in rainbow trout muscles. We treated rainbow trouts with different concentrations of deltamethrin (0.25 microg/L, 1 microg/L and 2.5 microg/L) and observed the alterations in mRNA expression levels of IGF-I, IGF-II and GH-I at different time intervals (at 6th, 12th, 24th, 48th, 72nd hours and 30th day). The mRNA levels significantly decreased with increasing deltamethrin concentrations for acute administration. Interestingly, a significant recovery in GH-I expression was seen after the 72nd hour up to 30th day while no significant differences were observed for IGF-I and IGF-II between the same time intervals. Here we demonstrate that deltamethrin exposure decreases the expression of IGF-I, IGF-II and GH-I in rainbow trout which might cause undesirable outcomes not only in growth, but also in development and reproduction.