Interpretation of cancer incidence and mortality rates in a defined population requires an understanding of multiple complex and interacting factors. These factors include the prevalence of risk factors in the population, changes in the use of medical interventions to screen and treat the disease, and changes in how data are collected and reported. Analyzing temporal trends in cancer incidence and mortality rates can provide a more comprehensive picture of the burden of the disease and generate new insights about the impact of various interventions. For example, assessing trends in breast cancer mortality rates over the past two decades may be informed by knowledge of the known risk factors for the disease, changes in mammography screening, and the dissemination of efficacious adjuvant therapies. In contrast to breast cancer, assessing recent trends in prostate cancer incidence and mortality presents more challenges because of limitations in the understanding of the causes of the disease, its natural history, and uncertainty about the efficacy of screening and treatment interventions. The etiology of prostate cancer is not clearly understood (see the review on" Medical History and Etiology of Prostate Cancer" in this issue of Epidemiologic Reviews). Until randomized trials now underway can be completed, the efficacy of prostate-specific antigen (PSA) screening of asymptomatic men remains uncertain (see the review on" Prostate Cancer Early Detection: a Clinical Perspective" in this issue of Epidemiologic Reviews). There has been controversy and disagreement about the relative efficacy of various management options for men diagnosed with clinically localized prostate cancer. Furthermore, the characteristics of the disease, such as the long latency period and the high prevalence of indolent tumors (see the review on" Natural History of Prostate Cancer: Epidemiologic Considerations"