Public health practice often requires locating individuals in the community. This article presents information on the methods and amount of time and effort required to locate over 2300 low-income and minority women in Maryland, New York, Ohio, and Texas for a mammography rescreening study. In 1999, we identified 2528 low-income women who had a mammogram in 1997 funded by the National Breast and Cervical Cancer Early Detection Program. Starting 30 months after that mammogram, we made numerous attempts to locate each woman while recording the number of calls, letters, and tracing attempts used and the date she was found. More than 93% of the women were located. On average, it took 73.8 days (range 1-492 days) and 7.2 calls and letters (range 1-48) to reach each woman. Locating women in racial and ethnic minority groups required more time and effort. About 10% of all located women were found only after our subject tracing protocol was implemented. The percentage of located women increased markedly with more months of effort and additional calls and letters. Because women who were more difficult to locate were less likely to have been rescreened, the mammography rescreening percentages at the end of the study were slightly lower than they would have been had we terminated location efforts after 1-3 months. Locating low-income women in the community is difficult, particularly when obtaining a high response rate from all groups is important. Terminating data collection prematurely may decrease minority group representation and introduce bias.