We assessed to what extent gay men are motivated to obtain vaccination against hepatitis B virus (HBV), as well as the social cognitive determinants of this motivation. A cross-sectional survey was conducted among homosexual men by means of a written questionnaire that contained assessments of intention, knowledge and social-cognitive determinants of intention (i.e. attitude, social norm and perceived behavioural control towards vaccination, perceived severity and perceived vulnerability regarding HBV infection). Four hundred and thirty-three homosexual men completed the questionnaire. We conducted a linear regression analysis to determine the contribution of social-cognitive variables in explaining intention to be vaccinated. Attitude, social norm and perceived vulnerability were significant predictors of intention. Usually, health education emphasizes the severity of a disease, but from this analysis we can conclude that gay men should be convinced of their personal vulnerability to HBV, the benefits of vaccination, and that important referents of the targeted person think positively about vaccination.