A case-control study was conducted to examine the relationship between Wilms' tumor and paternal occupational exposures. The case group consisted of 200 children diagnosed as having Wilms' tumor who were registered at selected National Wilms' Tumor Study institutions during the period June 1, 1984, to May 31, 1986. Disease-free controls were matched to each case using a random digit dialing procedure. The parents of cases and controls completed a self-administered questionnaire. There was no consistent pattern of increased risk for paternal occupational exposure to hydrocarbons or lead found in this study. However, certain paternal occupations were found to have an elevated odds ratio (OR) of Wilms' tumor, including vehicle mechanics, auto body repairmen, and welders. Offspring of fathers who were auto mechanics had a 4- to 7-fold increased risk of Wilms' tumor for all 3 time periods. The largest increased odds ratio for auto mechanics was in the preconception period [OR = 7.58; 95% confidence interval (CI) = 0.90-63.9]. Welders had a 4- to 8-fold increased odds ratio, with the strongest association during pregnancy (OR = 8.22; CI = 0.95-71.3). Although chance cannot be excluded as a possible explanation, association of Wilms' tumor with these occupations has been reported in previous studies. Further study is needed to provide data on the specific occupational exposures involved.