This article evaluates the potential epidemiologic uses of capture-recapture, which include the primary area of determining disease frequency. Capture-recapture may be a means to effectively "count" new cases (incidence) or count existing cases (prevalence). Specific applications of capture-recapture in epidemiology are presented, one of which is its use in estimating death rates in a region close to Calcutta, India. The method also has considerable potential to assess suicides, and it may be the only technique to assess disease frequency in developing countries. In addition to generating an estimate of population size, another application of capture-recapture is to assess the costs of ascertainment relative to the degree of accuracy. This approach provides a formal means for assessing the cost-benefits of lists for the identification of cases. The authors believe that with careful and appropriate use, capture-recapture methods will provide a new approach that can considerably improve our ability to monitor disease.