ObjectiveProeating disorder (pro-ED) communities online encourage harmful weight-loss and weight-control practices. This study examined the association between exposure to pro-ED content online and subjective well-being (SWB) among adolescents and young adults in four countries. MethodCross-national data were collected in the US, Germany, the UK and Finland from Internet users aged 15-30 years (N=3,557; 50.15% male). The questionnaire assessed SWB, exposure to harm-advocating websites, online activity, prior victimization, and social belonging. Ordinary least squares (OLS) regression models assessed the relationship between SWB and pro-ED exposure and adjusted for a number of confounding factors. ResultsOf the participants, 17% had been exposed to pro-ED content (US 20%, Germany 7%, UK 21%, Finland 22%). Exposure to pro-ED content online was negatively associated with SWB in the US, Germany, and Finland, also after adjusting for the confounding factors. Offline social belonging moderated the association between pro-ED and SWB. DiscussionParticipants who visited pro-ED websites reported lower SWB than others did. The potentially harmful impact of visiting these sites was buffered by the strong offline social belonging. Given the observed similarities across the countries, it is important for families, health professionals, and educators to stay abreast of online communities that have possible contra recovery influences and to be able to discuss such Internet contents in a way that increases treatment motivation. (c) 2016 Wiley Periodicals, Inc. (Int J Eat Disord 2017; 50:50-57)