The introduction of PSA testing into clinical practice has revolutionised the diagnosis and management of prostate cancer, although much debate surrounds the value of PSA testing. Despite the lack of definitive evidence, there is widespread use of PSA screening in asymptomatic men, with aggressive investigation and treatment recommended. This has undoubtedly led to overdiagnosis and overtreatment of some men with prostate cancer. This book summarises the basis and clinical aspects of PSA testing and prostate cancer diagnosis. Additionally, data from a unique population-based database of PSA tests are presented examining the utility of a single PSA and of repeated measures of PSA in the diagnosis of prostate cancer. Finally, by means of an exceptional natural experiment in Northern Ireland, the natural history of an elevated PSA without invasive investigation is explored. This book will be useful for men, students and physicians alike who wish a concise but comprehensive text on PSA and prostate cancer diagnosis, and will help inform men when trying to make the difficult decision about proceeding to invasive investigaton and treatment.