The insulin family of growth factors (insulin, Insulin-like Growth Factor (IGF)-1, and IGF2) are essential for testicular function and sex determination. The IGF system mediates the proliferation of steroidogenic cells; however, the intratesticular source of the IGF system ligands (IGF-1 and IGF-2) required for the proliferation of steroidogenic cells have not been studied. To investigate the IGF system, we inactivated either the Igf1 or Igf2 genes, or both together, in all the somatic compartments using the Cre/LoxP system with the Wt1 promoter. Our genetic evidence shows that mutant mice exhibit a testis:body-weight ratio reduction and an anogenital index reduction. However, mice remained fertile and produced the same number of pups per litter compared to the controls. Moreover, we failed to delete Igf1; only Igf2 was successfully deleted in all the somatic cells. These observations suggest that Igf2 appears to be dispensable for fertility. However, our results did lead to the discovery that the Igf1 gene cannot be deleted in the mouse lines that we used.