Prostate cancer, the most frequent non-cutaneous malignancy in aging men, is a growing medical problem, representing the second leading cause of male cancer deaths. Despite its high morbidity, the etiology of prostate cancer remains largely unknown. Several studies have documented hormonal imbalance, such as alteration in androgens and estrogens, obesity, family history and growth factors, as risk factors in the pathogenesis of prostate cancer. Insulin is a growth-promoting hormone that is reported to be involved in the pathogenesis of various malignancies, such as breast and bladder cancers. Insulin is known to increase cancer risk through its effect on cell proliferation, differentiation and apoptosis. In the last decade, converging evidence from epidemiological and clinical studies suggests that the insulin is involved in the tumorigenesis and neoplastic growth of the prostate. Several mechanisms have been suggested to explain the possible causal relationship between insulin and prostate cancer, such as the sympathoexcitatory effect of insulin, alteration of sex hormone metabolism, insulin-like growth factor pathway, signal transduction mechanism and dyslipidemia. The present paper reviews relevant existing studies related to the role of insulin in the pathogenesis of prostate carcinoma.