A mortality study of workers employed between 1944 and 1977 at an electrical capacitor manufacturing plant where polychlorinated biphenyls (PCBs), chlorinated naphthalenes, and other chemicals were used was undertaken. Age, gender, and calendar year-adjusted standardized mortality ratios (SMRs) were calculated for 2885 white workers. Although individual exposure assessment was limited, PCBs alone or in combination with other chemicals could be associated with increased risks for liver/biliary, stomach, intestinal, and thyroid cancer.