Estimates of the size and the growth of the unauthorized migrant population in the United Status have important and far-reaching public policy implications. Such estimates influence assessments of the impact of unauthorized migrants on local labor markets, public welfare resources, school enrollments, and demand for health services. The size of this clandestine population also affects evaluations of U.S. immigration laws, border enforcement policies and the future impact of U.S. immigration and naturalization law. For instance, reliable estimates made during the early 1980s of the unauthorized population helped to predict the likely number of persons seeking legalization under the provisions of the Immigration Reform and Control Act (IRCA) (GAO, 1993; Passel and Woodrow, 1987). Nevertheless, the unauthorized migrant population is difficult to measure directly. Data obtained from survey items about legal status may be highly questionable if not worthless because unauthorized migrants wishing to escape 512 detection may be unlikely to reveal their status in interviews and/or questionnaires. However, indirect demographic methods for estimating the unauthorized migrant population have been developed and refined over the past twenty years. These efforts have, for the most part, yielded increasingly reliable estimates