RESUMEN
To evaluate a reported five-fold increase in leukaemia mortality among workers exposed to ionising radiation at Portsmouth (New Hampshire) Naval Shipyard (PNS), a retrospective cohort mortality study of all PNS civilian workers employed from 1952 to 1977 was done. Three subcohorts were identified: 7615 workers with radiation exposure of 0.001 to 91.414 rem (mean 2.779 rem, median 0.545 rem), 15 585 non-radiation workers, and 1345 workers selected for radiation work who received no measurable exposures. Vital status on 96% of the workers was ascertained and observed mortality due to all causes, all malignant neoplasms, and malignant neoplasms of the lymphatic and haematopoietic tissues, including leukaemia, was compared with that expected from mortality-rates for United States White males. Leukaemia mortality in radiation and non-radiation workers at PNS was also compared. Although the study had a power of greater than 99% to detect statistically a five-fold increase in leukaemia mortality among the radiation workers, and a power of 67% to detect a two-fold increase, there was no excess due to leukaemia or any other cause. The standardised mortality ratio for leukaemia among radiation workers was 84 (95% confidence interval, 34--174). There was no dose-response relation with radiation or any increased mortality in radiation over non-radiation workers. The study was, however, limited by short latency (time since first radiation); only 53% of the workers had less than 15 years' latency.