ObjectiveTo assess the acceptability and impact of anti-smoking policies in three prisons in Switzerland. MethodsA before–after intervention study in A) an open prison for sentenced prisoners, B) a closed prison for sentenced prisoners, and C) a prison for pretrial detainees. Prisoners and staff were surveyed before (2009, n=417) and after (2010–2011, n=228) the interventions. Medical staff were trained to address tobacco dependence systematically in prisoners. In prison A, a partial smoking ban was extended. No additional protection against second-hand smoke was feasible in prisons B and C. ResultsIn prison A, more prisoners reported receiving medical help to quit smoking in 2011 (20%) than in 2009 (4%, p=0.012). In prison A, prisoners and staff reported less exposure to second-hand smoke in 2011 than in 2009: 31% of prisoners were exposed to smoke at workplaces in 2009 vs 8% in 2011 (p=0.001); in common rooms: 43% vs 8%, (p<0.001). No changes were observed in prisons B and C. ConclusionsReinforcement of non-smoking rules was possible in only one of the three prisons but had an impact on exposure to tobacco smoke and medical help to quit. Implementing anti-smoking policies in prisons is difficult in the absence of appropriate legislation.