the Federal Office for Public Health (OFSP) mandated the University Institute of Social and Preventive Medicine (IUMSP) to evaluate the national campaign ‘Break The Chain’ carried out in April 2012. It is an HIV/AIDS prevention campaign aimed exclusively at men who have sex with men (MSM). It was implemented by Checkpoint Zürich and Checkpoint Geneva with the support of Swiss AIDS Aid (SSA) under the mandate of the OFSP.