Introduction:Successful smoke-free legislation is dependent on political will, enforcement and societal support. We report the success and pitfalls of a non-enforced nationwide smoke-free legislation in Greece, as well as ways in which compliance and enforcement-related factors, including ashtrays and signage, may impact indoor secondhand smoke (SHS) concentrations.Methods:A follow-up study of venues (n = 150, at baseline, n = 75 at 2-year follow-up) in Greece assessed indoor particulate matter with a diameter less than 2.5 micrometers (PM2.5) concentrations attributable to SHS smoke every six months for two years (n = 455 venue/measurements).Results:Following the implementation of the 2010 smoke-free legislation, mean PM2.5 concentrations attributable to SHS fell from 175.3 μg/m3 pre-ban to 84.52 μg/m3 immediately post-ban, increasing over subsequent waves (103.8 μg/m3 and 158.2 μg/m3 respectively). Controlling for potential influential factors such as ventilation, time of day, day of week, city and venue type, all post-ban measurements were still lower than during the pre-ban period (Wave 2 beta: -118.7, Wave 3 beta: -87.6, and Wave 4 beta: -69.9). Outdoor or indoor signage banning smoking was not found to affect SHS concentrations (beta: -10.9, p = 0.667 and beta: -18.1, p = 0.464 respectively). However, ashtray or ashtray equivalents were strong determinants of the existence of indoor SHS (beta: +67 μg/m3, p = 0.017).Conclusions:While the public may be supportive of smoke-free legislation, adherence may decline rapidly if enforcement is limited or nonexistent. Moreover, enforcement agencies should also focus on the comprehensive removal of ashtray equivalents that could act as cues for smoking within a venue.