This study assessed cognitive and affective predictors of intention to obtain vaccination against the hepatitis B virus (HBV) among men who have sex with men (MSM), based on leading social cognitive models of health behavior. The key predictors of vaccination intention were perceived risk of contracting HBV, expectancies regarding the outcome of vaccination, and the interaction between risk perception and outcome expectancies. Negative affect increased risk perceptions, which, in turn, positively affected vaccination intention. It is concluded that MSM should feel they are at risk for HBV, and see solutions to this risk. Copyright © 2008 SAGE Publications.