Cause specific mortality was studied in nuclear workers from five nuclear facilities in Belgium and compared to the general population. For the 1969-1994 period, mortality in male nuclear workers is significantly lower for all causes of death and for all cancer deaths. The same conclusions are reached if one assumes a latency period of 20 y between the first irradiation and cancer induction. In female workers, mortality due to all causes and all cancer deaths is not different from that of the general population. Analysis of cause specific mortality was performed for male and female workers for three endpoints: specific cancer sites, cardiovascular and respiratory diseases. No significant increase in mortality was observed. In male workers, the influence of cumulative dose was also investigated using four dose levels: no significant correlation was found. Smoking habits may be a confounding factor in smoking related health conditions.