In conclusion, in this first analysis of cancer incidence using data from the National Dose Registry of Canada, a number of associations with occupational exposure to ionizing radiation were noted. In the light of results from previous studies, our findings for the cancers of the thyroid and testis are of particular note. In the search for an explanation for the high standardized incidence ratio for thyroid cancer, solid occupational radioiodine exposure data could be helpful in assessing the possibility of this type of exposure's being a risk factor. A nested case-control study based on the cases of this study may also shed some light on the matter. In order to get a better interpretation of the high excess relative risk for testicular cancer, one may want to include the analysis of this type of cancer specifically in future studies rather than folding it into “miscellaneous cancers