Prostate cancer is one of the most common malignant tumors in Western countries. The etiology of prostate cancer is currently unknown, but it has been suggested that growth factor abnormalities may be involved in initiation and progression of this disease. Insulin-like growth factors (IGFs), including IGF-1 and IGF-2, are mitogenic peptides involved in the regulation of cell proliferation, differentiation and apoptosis. Studies have shown that IGFs are potent mitogens for a variety of cancer cells including prostate cancer since they stimulate cancer cell growth and suppress programmed cell death. This review outlines elements of IGF pathophysiology, reviews recent evidence that circulating IGF-1 levels are related to prostate cancer risk and discusses the clinical implications of these lines of research with respect to prevention and treatment.