Introduction - Between 2005 and 2007, the Chikungunya virus (CHIKV) caused a massive outbreak on Réunion Island, which peaked in February 2006. Whole blood collection was suspended on the island in January 2006. Methods - Estimates of the risk of CHIKV contamination in blood donations in Réunion were calculated for different phases of the epidemic based on incidence data, the average duration of asymptomatic viremia, and the proportion of asymptomatic cases. The estimated risk was compared with the results of viral genomic screening implemented on platelet donations. Results - The average risk was estimated at 132 per 100,000 donations for the entire epidemic, reaching a maximum of 1,500 per 100,000 at the peak of the epidemic. In total, 47 donations could have been contaminated if collection had not been suspended. Meanwhile, the estimated number of residents infected through vector-borne transmission was 312,500. The estimated risk (0.7%) and the observed risk in platelet donations (0.4%) were similar. Conclusion - The risk of contamination of a donation was high, but low compared to the risk of contamination via vector-borne transmission. Results consistent with the observed risk support these estimates. (R.A.)