Introduction. A case-control study recently showed that recipients of blood transfusions may have an increased risk of developing sporadic Creutzfeldt-Jakob disease (CJD), suggesting that blood donors in the silent preclinical phase could transmit the CJD agent. Method. We developed a model to estimate the number of blood donors likely to be in the preclinical phase of CJD at the time of blood donation, based on several assumptions regarding the duration of infectivity before the onset of the first clinical signs. The age- and sex-specific distributions of CJD cases, the blood donor population, the general population, and mortality in the general population were used in the model. Results. Between 1999 and 2008, the model estimates that, each year at the time of donation, an average of 1.1 (standard deviation (SD) = 0.3) donors would be in the preclinical phase of CJD if the infectious period were 1 year, 6.9 (Ã=0.5) if the infectious period were 5 years, 18.0 (Ã=0.6) if it were 10 years, and 33.4 (Ã=1.1) if it were 15 years. Conclusion. The estimated number of blood donors in the preclinical stage of CJD is limited. This result, along with the lack of a global increase in the number of CJD cases over time, supports the view that the risk of CJD transmission via transfusion, if it exists at all, is very low. (R.A.)