Background In France, men who have sex with men (MSM) are permanently deferred from donating blood. This measure, viewed by some as discriminatory, is the subject of public debate. Furthermore, it is not fully enforced, as some MSM do not disclose their sexual practices prior to donation. Methods We estimated the proportion of the current risk of HIV transmission via transfusion attributable to MSM. We then constructed a model based on data from behavioral and epidemiological surveys to assess the impact of a new strategy that would exclude only MSM who have had multiple sexual partners in the past 12 months. Results Twenty-eight HIV seroconversions occurred among regular donors between 2008 and 2010, representing a risk of 1 in 2,900,000 donations. Fourteen seroconversions (50%) involved MSM. If all MSM had refrained from donating blood, this risk would have been 1 in 5,700,000 donations, or half the current risk. The new strategy would result in an overall risk of HIV transmission ranging from 1 in 3,500,000 (close to the current risk) to 1 in 700,000 donations (four times higher than the current risk). Conclusion Modifying the current deferral policy for MSM may increase the risk of HIV transmission through transfusion. However, the model does not account for the potential improvement in compliance among MSM with a less stringent policy that would be perceived as more equitable. Conversely, relaxing this policy could encourage some MSM to get tested when donating blood. Therefore, qualitative studies should be conducted to assess the motivations of MSM who currently donate blood despite the deferral policy, as well as potential changes in their adherence to a new strategy. (R.A.)