In considering the basic statistics underlying elimination disorders, it is essential to first define the epidemiological concept of prevalence. Prevalence denotes the rate of a disease in a given population. Often prevalence rates are utilized to convey the likelihood or commonality of a disease or condition (e.g., percentage of the population, proportion of cases in a clinical sample). This entry discusses the prevalence rates for two main categories of elimination disorders: (1) enuresis (i.e., involuntary urination) and (2) encopresis (i.e., involuntary defecation).