PURPOSE: The Farm Family Exposure Study was initiated to characterize pesticide exposure to farm family members around the time of one pesticide application in a manner that will facilitate exposure assessment in epidemiologic studies of pesticides. METHODS: A sample of farm families with children was recruited by randomly selecting farmers from lists of licensed pesticide applicators in Minnesota and South Carolina. Eligible families were selected from among those who planned to apply one of three chemicals, glyphosate, 2,4-D, or chlorpyrifos, as part of their normal operations. The applicator, spouse, and all children in the family ages 4-17 years were included in the study. The applicator and spouse completed self-administered questionnaires addressing demographics, farming practices and potential exposures to them and their children. Field observers documented the application, recorded application practices, equipment, potential exposures, and the presence of children or spouses in the immediate vicinity of pesticide activities. All study participants were asked to collect each urine void for 5 days, 1 day before through 3 days after the application. Pesticides were measured in 24-h composite urine samples with a one part per billion limit of detection. RESULTS: Of 11,164 applicators screened, 994 families met the inclusion criteria. Of these, 95 families were enrolled. Enrollees were similar in most characteristics to their peers who were not participants in the study. In total, there were 106 applications, 10 of which involved more than one chemical. This resulted in urinary data for 48 farmers and spouses and their 79 children for glyphosate, 34 farmers and spouses and their 50 children for chlorpyrifos, and 34 farmers and spouses and their 53 children for 2,4-D. Compliance with the 24-h urine collection was particularly good for the adult participants. There were more missing samples for children than for adults, but overall compliance was high. CONCLUSION: The Farm Family Exposure Study should provide insights about pesticide exposure under real world conditions and thereby facilitate improved exposure assessment in epidemiologic studies of agricultural populations.