Background Pesticides, which encompass a wide range of chemicals, are used extensively worldwide to control weeds, insects and other pests, both agriculturally, and in other settings, and have been linked to numerous adverse health outcomes, including cancer. Use has increased dramatically in the last several decades, but establishing a link between specific pesticide active ingredients and disease can be challenging.

Methods The Agricultural Health Study is a prospective cohort study of 57,310 licensed pesticide applicators and 32,345 of their spouses in Iowa and North Carolina, USA. At enrollment in 1993-1997, participants provided information on mixing, loading and applying individual pesticide active ingredients over their lifetimes. At subsequent interviews, they provided information on chemical products used on specific crops and animals. This self-reported use has been shown to be generally reliable. In addition, farm characteristics and practices allow for the assessment of potential non-occupational exposures for spouses not working on the farm. Incident cancers are identified through regular linkage to the cancer registries in each state.

Results Results from this study have indicated associations between specific pesticides and several cancer sites, including cancers of the prostate, lung and lymphohematopoietic malignancies. Ongoing analyses are focused on the re-evaluation of previously observed associations, as well as initial investigations of newer and less commonly used chemicals, as well as rarer tumours. Preliminary results of these evaluations have suggested increased risk with specific pesticides and tumours such as liver and ovary. In addition, the evaluation of risks related to non-occupational pesticide exposures is a new area of emphasis.

Conclusions This study provides a unique opportunity to investigate both occupational and non-occupational exposures to specific pesticides and cancer risk in a prospective setting.