We examine mortality in a cohort of workers at the Oak Ridge National Laboratory (ORNL), a US Department of Energy research and development facility. The last mortality follow-up of this epidemiologically important cohort was conducted 18 years ago and included workers hired between 1943 and 1972. Analyses of these data revealed a positive association between occupational radiation dose and all cancer mortality under a 20-year lag assumption (1.73% increase in all cancer mortality per 10 mSv, standard error = 0.86). We have expanded this cohort to include 22,834 workers hired between 1943 and 1985, and updated mortality follow-up through 2008, yielding almost three times the number deaths observed in the last mortality follow-up of an ORNL cohort. Extending follow-up of this cohort is important not just for statistical power, but also because many important questions in radiation research concern the long term effects of irradiation, particularly on malignant diseases. These workers were individually badge-monitored for external exposure to ionising radiation, allowing evaluation of the effects of protracted radiation exposures accrued at work. We compared the observed deaths to expectations based upon US mortality rates, and evaluated radiation dose-mortality associations. Findings include excess deaths due to cancer of the pleura (SMR = 12.09 95%CI: 4.44, 26.32), cancer of the bladder (SMR = 1.89 95%CI: 1.26, 2.71), and leukaemia (SMR = 1.33 95%CI: 0.87, 1.93) among hourly-paid males, and excess deaths due to cancer of the bladder (SMR = 2.20 95%CI: 1.20, 3.69) and leukaemia (SMR = 1.64 95%CI: 1.09, 2.36) among females. Further results will be presented.