Previous studies have evaluated prostate cancer in farm-working populations and most, although not all, have found an elevated risk of this cancer in farmers and farm workers. Specific occupational risk factors have not been identified. A nested case-control study of prostate cancer was conducted within a large cohort of a predominantly Hispanic labor union in California, the United Farm Workers of America. By conducting an electronic record linkage between a roster of the union members and the California Cancer Registry for the years 1988 through 1999, newly diagnosed cases of prostate cancer were identified within the union. Age-matched controls were randomly selected from the remainder of the cancer-free cohort. Risk for prostate cancer was examined by examining the type of crops and commodities cultivated by the farm workers as well as by the date of first union activity and duration of union affiliation. In addition, the risk of prostate cancer was evaluated in association with use of several pesticides recorded by the California Department of Pesticide Regulation. Between 1988 and 1999, 222 newly diagnosed prostate cancer cases were identified for analysis and 1110 age-matched controls were selected. The risk of prostate cancer was not associated with patterns of employment in any crop/commodity. Increasing duration of union affiliation was associated with decreasing prostate cancer risk. Although risk was not associated with total pounds of pesticides applied in the years and counties where farm workers were employed, risk was increased with specific chemicals, including simazine, lindane, and heptachlor, and suggestive increases were observed with dichlorvos and methyl bromide. We concluded that Hispanic farm workers with relatively high levels of exposure to organochlorine pesticides (lindane and hepatachlor), organophosphate pesticides (dichlorvos), fumigants (methyl bromide), or triazine herbicides (simazine) experienced elevated risk of prostate cancer compared to workers with lower levels of exposure.