Prostate cancer, the most frequent non-cutaneous malignancy in men from industrialized countries, is a growing medical problem, representing the second leading cause of male cancer deaths. In the last decade, converging evidence from epidemiological and biological studies suggests that the Insulin-like Growth Factor (IGF) axis is involved in the tumorigenesis and neoplastic growth of prostate cancer. Epidemiological observations indicated that circulating IGF-I levels are positively associated with the increased risk of prostate cancer. The activation of type I IGF receptor (IGF-IR) by IGF-I and/or IGF-II, has mitogenic and antiapoptotic effects on normal and malignant prostate cells. Altered expression of IGF axis components has also been reported in vitro and in animal models of prostate cancer, as well as in human prostate cancer tissue samples. In this review we address and analyze epidemiological studies, in vitro and in vivo cancer models, and human ex vivo prostate cancer researches performed to date supporting the role of IGF axis in prostate cancer.