Abstract PURPOSE: To describe the procedures used in tracing members of a prospective urban birth cohort, and to present preliminary tracing results. METHODS: The subjects selected for this study were among former participants in the Columbia Presbyterian Medical Center's cohort of the National Collaborative Perinatal Project. Selection criteria included availability of postnatal growth data at age 7, female gender and racial/ethnic categorization of White, Black or Puerto Rican for the offspring. Mothers were traced in order to obtain permission and information regarding their children's whereabouts. Tracing information was last updated over 30 years ago. Data used for tracing included mother's name, last known address, date of birth and Social Security Number (when available). Free nationwide telephone directories and fee-based internet services were utilized to search and obtain current residential information. RESULTS: The final sample for tracing consisted of 809 mother and daughter pairs. Over a period of 12 months, we have attempted to trace 506 (62%) mothers. Of this number, 223 (44%) were Black, 148 (29%) were White and 135 (27%) were Puerto Rican. Social Security Numbers were available for 269 (53%) mothers. Availability of social security number did not differ significantly by racial/ethnic group. To date, 274 (54%) are still in the process of being traced, 196 (39%) have been successfully traced, and 36 (7%) could not be traced. Mothers of Puerto Rican descent were less likely to be traced than white and black mothers. Regardless of ethnicity, mothers whose Social Security Numbers were available were more likely to be traced than mothers without Social Security Numbers. CONCLUSION: Our preliminary findings suggest that long-term tracking of a mobile urban population can be accomplished through free and low-cost internet-based resources.