OBJECTIVE: To investigate site-specific condom-use norms as assumed by visitors of gay venues and websites across The Netherlands and their association with men’s own use of condoms. METHODS: In 2010, men who have sex with men (MSM) visiting 18 sex venues (e.g., saunas), 30 nonsex venues (e.g., bars), 6 dating websites, and 2 social network websites completed an on-site questionnaire measuring 2 site-specific norms concerning anal sex: descriptive (assumed condom use of others at venue or website) and injunctive (assumed approval of condom use by others at venue or website). We measured the association between assumed descriptive norms and own use of condoms using logistic regression. RESULTS: Among 2,376 participants (median age = 30 years; IQR = 22-43), 62% (n = 1,483) assumed that other visitors would not use condoms. Among men self-reporting on their own use of condoms, 22% (318/1,421) reported condomless anal sex. Men at nonsex venues assumed other visitors would use condoms more often and approved of using them more often compared to men at sex venues. At all sites (venues/websites), men who assumed that others did not use condoms were more likely to have condomless sex themselves. CONCLUSIONS: At gay sites across The Netherlands, more than half of MSM believed visitors of these sites would not use condoms during anal sex. The perception that others would not use condoms was associated with less own condom use. HIV prevention should address problematic on-site condom-use norms, as they play a role in influencing sexual behavior between men that meet at these sites.