A 40-year follow-up study was conducted to examine mortality among 1,664 patients in Japan suffering from “Yusho,” a disease caused by ingestion of rice oil contaminated with polychlorinated biphenyls and polychlorinated dibenzofurans. To evaluate the effects of exposure on mortality, the authors calculated standardized mortality ratios. National mortality rates for major causes of death were used as reference points. A total of 1,596 Yusho patients (95.9%) were followed until death or the end of the study (December 31, 2007). The standardized mortality ratios for most major causes of death were not significantly elevated, with the exceptions of all types of cancer (standardized mortality ratio (SMR) = 1.37, 95% confidence interval (CI): 1.11, 1.66), liver cancer (SMR = 1.82, 95% CI: 1.06, 2.91), and lung cancer (SMR = 1.75, 95% CI: 1.14, 2.57) in males. In addition, the standardized mortality ratios for all cancers, liver cancer, and lung cancer among males tended to decrease over time. Results from this study suggest that the carcinogenicity of polychlorinated biphenyls and polychlorinated dibenzofurans must be taken into account when evaluating mortality risk.