We estimate that there were 8.7 million illegal aliens in the March 2003 CPS. It must be remembered that this estimate only includes illegal aliens captured by the March CPS, not those missed by the survey. By design this estimate is very similar to those prepared by the Census Bureau, the former Immigration and Naturalization Service (INS), and the Urban Institute. Although it should be obvious that there is no definitive means of determining whether a respondent in the survey is an illegal alien, the findings in this study are consistent with previous research. For example, the Urban Institute estimated that in 2002 Mexicans accounted for 57 percent of the illegal population; our method finds 58 percent in 2003. Using 2003 data, we estimate that 88 percent of illegals arrived after 1990; the Urban Institute estimated 85 percent using 2002 data. Our results also produce estimates that are similar in other areas, such as age and workforce participation.