The Agricultural Health Study (AHS) is a prospective study of cancer and other health outcomes in addition to cancer in a cohort of licensed pesticide applicators and their spouses from Iowa and North Carolina. The objective of the study is to examine how agriculture, lifestyle and genetic factors affect the health of farming populations. More than 89,000 farmers and their spouses in Iowa and North Carolina were enrolled between 1993 and 1997. Since enrollment, follow‐up questionnaires have been conducted to update various exposures and health outcomes among the cohort. In addition, the cohort is regularly linked to disease and mortality registries. The AHS is funded by the National Cancer Institute and the National Institute of Environmental Health Sciences in collaboration with the United States Environmental Protection Agency. In the sixth phase of the AHS contract, the Contractor shall serve as the coordinating center for all study activities.