Stress urinary incontinence (SUI) has an observed prevalence of between 4% and 35%. Whereas the clinical definition of SUI has been established by the International Continence Society, the epidemiologic definition has not been established, leading to a broad disparity in reported prevalence rates. Numerous risk factors for SUI have been identified. Aging, obesity, and smoking appear to have consistent causal relationships with the condition, whereas the roles of pregnancy and childbirth remain controversial. The prevalence of many of these risk factors is increasing in the adult female population of the United States. These population changes, combined with increasing physician awareness and the availability of nonsurgical therapy, will likely increase the number of women receiving care for SUI over the next 3 decades.