surrogate groups. We looked at three principal causes of mortality: all-cause, all-cancer, and leukemia, hypothesizing that increases in the latter two could result from radiation exposure. For descriptive purposes we also present comparisons between participants and the comparison group for 44 other disease categories. Findings stated in this report follow.

• Among Navy personnel, the primary analysis group for this study, we found that participants at the CROSSROADS nuclear test experienced higher mortality than a comparable group of nonparticipating military controls. The increase in all-cause mortality was 4.6 percent (relative risk [RR] = 1.046, 95% confidence interval, 1.020–1.074) and was statistically significant (p < 0.001).² For malignancies, the elevation of mortality was lower—RR = 1.014 (0.96–1.068)—and was not statistically significant (p = 0.26). Similarly, leukemia mortality RR was elevated to 1.020 (0.75–1.39), but not significantly (p = 0.90) and by less than all-cause mortality. The increase in all-cause mortality did not appear to concentrate in any of the disease groups we considered. Of the 44 other specific cancers and disease categories we examined, there were no statistically significant increases in mortality. The overall elevation of mortality rate ratios for malignancies and leukemias in the participants were not statistically significant and, in fact, were lower than for many other causes of death.
• Navy mortality due to all malignancies and leukemia did not vary substantially among our exposure surrogate groups (i.e., those who boarded target ships after a detonation vs. those who did not, and those enlisted personnel who had an Engineering & Hull occupational specialty vs. those in other specialties).
• Participants who boarded target ships were thought to be more highly exposed than the rest of the participant group. Relative to the controls (nonparticipating comparison group), boarding participants experienced a 5.7 percent increase in all-cause mortality, RR equal to 1.057 (1.014–1.10), p = 0.0093, whereas the nonboarders (less exposed participant group) experienced a 4.3 percent increase (RR = 1.043 [1.015–1.073], p = 0.0028). Aside from all-cause mortality, risks for boarding participants did not significantly exceed those for controls for any of the disease categories, and risks relative to controls were similar for boarding and nonboarding participants. The increase in risk for all-malignancies among the participants was 2.6 percent (RR = 1.026 [0.94–1.12], p = 0.55) for boarders and 1 percent (RR = 1.010 [0.95–1.068], p = 0.73) for nonboarders. For leukemia, the increase in mortality risk for boarders was, 0.7 percent (RR = 1.007 [0.61–1.66], p = 0.98) and for nonboarders, 2.4 percent (RR = 1.024 [0.737–1.422], p = 0.89). In all cases the 95% confidence intervals