The long term health effects of occupational exposure to polychlorinated-biphenyls (1336363) (PCBs) were studied. The vital status of 2,567 workers occupationally exposed to PCBs for a minimum of 3 months was determined, and a standardized mortality ratio (SMR) was determined based on the observed to expected mortality ratio of the worker cohort and the corresponding United States White male and female cause specific mortality rates. SMRs for deaths from all malignant neoplasms, nervous system disease, circulatory system disease, accidents, all other causes, and all causes combined were 89, 88, 95, 71, 89, and 89, respectively, for the cohort of all PCB exposed workers. Mortality in the cohort for cancer of the rectum and liver was excessive but not statistically significant. The only significant SMR difference occurred in number of rectal cancer deaths among female PCB exposed workers from one of the surveyed manufacturing facilities, where 3 rectal cancer deaths were observed and 0.5 were expected. There was no relationship between total PCB exposure and mortality. The authors conclude that the small number of deaths among PCB workers makes the conclusions of this study tentative. They suggest that the slight excess of liver cancer in the cohort is consistent with previously reported PCB effects in animals.