ObjectivesThis paper aims to estimate the percentage of European men who have sex with men (MSM) who may benefit from pre-exposure prophylaxis (PrEP), applying the three most widely used HIV risk indices for MSM (MSM Risk Index, Menza score, San Diego Early Test (SDET) score) and drawing on a large-scale multisite bio-behavioural survey (Sialon II).MethodsThe Sialon II study was a bio-behavioural survey among MSM implemented in 13 European cities using either time-location sampling or respondent-driven sampling. Biological and behavioural data from 4901 MSM were collected. Only behavioural data of HIV-negative individuals were considered. Three widely used risk indices to assess HIV acquisition risk among MSM were used to estimate individual HIV risk scores and PrEP eligibility criteria.Results4219 HIV-negative MSM were considered. Regardless the HIV risk score used and the city, percentages of MSM eligible for PrEP were found to range between 5.19% and 73.84%. Overall, the MSM Risk Index and the Menza score yielded broadly similar percentages, whereas the SDET Index provided estimates constantly lower across all cities. Although all the three scores correlated positively (r>0.6), their concordance was highly variable (0.01<CCC<0.62).ConclusionOur findings showed the impact of different scoring systems on the estimation of the percentage of MSM who may benefit from PrEP in European cities. Although our primary aim was not to compare the performance of different HIV risk scores, data show that a considerable percentage of MSM in each city should be offered PrEP in order to reduce HIV infections. As PrEP is highly effective at preventing HIV among MSM, our findings provide useful, practical guidance for stakeholders in implementing PrEP at city level to tackle HIV infections in Europe.