Exposure to certain pesticides has been linked with both acute and chronic adverse health outcomes such as neurotoxicity and risk for certain cancers. Univariate analyses of pesticide exposures may not capture the complexity of these exposures since use of various pesticides often occurs simultaneously, and because specific uses have changed over time. Using data from the Agricultural Health Study, a cohort study of 89,658 licensed pesticide applicators and their spouses in Iowa and North Carolina, we employed factor analysis to order to characterize underlying patterns of self-reported exposures to 50 different pesticides. Factor analysis is a statistical method used to explain the relationships between several correlated variables by reducing them to a smaller number of conceptually meaningful, composite variables, known as factors. Three factors emerged for farmer applicators (N=45,074): (1) Iowa agriculture and herbicide use, (2) North Carolina agriculture and use of insecticides, fumigants and fungicides, and (3) older age and use of chlorinated pesticides. The patterns observed for spouses of farmers (N=17,488) were similar to those observed for the farmers themselves, whereas five factors emerged for commercial pesticide applicators (N=4,384): (1) herbicide use, (2) older age and use of chlorinated pesticides, (3) use of fungicides and residential pest treatments, (4) use of animal insecticides, and (5) use of fumigants. Pesticide exposures did not correlate with lifestyle characteristics such as race, smoking status or education. This heterogeneity in exposure patterns may be used to guide etiologic studies of health effects of farmers and other groups exposed to pesticides.