The number of patients who seek treatment with complementary and alternative medicine has increased during the past decade. The trend is primarily driven by consumers who start to change their views toward conventional pharmaceutical approaches that are offered to them. Among all complementary and alternative therapies used in the management of prostate cancer, Prostate Cancer-SPES (PC-SPES) has attracted much national attention because of its potency, controversy, and recall by the US Food and Drug Administration. PC-SPES contains extracts from a mixture of eight common herbs that have been used for thousands of years. This article is devoted to reviewing the basic and clinical data of using PC-SPES in prostate cancer therapy. It also explores the difference in philosophies between Western medicine and herbal medicine and explains the inherent difficulties in evaluating herbal medicine. The article concludes that PC-SPES cannot be evaluated by the same standards established to test synthetic pharmaceutical compounds. Thus, new standards need to be developed for the evaluation of herbal medicine.