People with or at risk for mpox are likely to be stigmatized because of analogies to other sexually transmitted infections. Stigma is driven by beliefs about the perceived severity of the condition and perceived responsibility for acquiring the condition, both in broader society and individual responsibility. We explored these beliefs and compared them across mpox, human immunodeficiency virus (HIV), syphilis, gonorrhoea, and chlamydia in an online survey, conducted in July 2022, with 394 men-who-have-sex-with-men in the Netherlands. We compared mean scores between infections using repeated measures analysis of variance and conducted hierarchical regression analyses to identify determinants of both mpox perceived responsibility endpoints. Results showed that participants expected that mpox would be seen as a "gay disease" and will be used to blame gay men. Compared to other infections, mpox was considered less severe than HIV, but more severe than syphilis, gonorrhoea, and chlamydia. Perceived responsibility was comparable across infections, but, for each infection, participants perceived attributed responsibility to be higher in society than individual responsibility. Both perceived responsibility endpoints were highly correlated with each other and with other stigma beliefs. These results provide insight on the underlying determinants of mpox stigma and demonstrate that anticipated mpox stigma is present in the Netherlands.