Introduction: On January 2, 2011, the Spanish government passed a new smoking law that banned smoking in hospital campuses. The objective of this study was to evaluate the implementation of smoke-free campuses in the hospitals of Catalonia based on both airborne particulate matter and observational data. Methods: This cross-sectional study included the hospitals registered in the Catalan Network of Smoke-free Hospitals. We measured the concentration of particulate matter < 2.5 μm in μg/m3 at different locations, both indoors and outdoors before (2009) and after (2011) the implementation of the tobacco law. During 2011, we also assessed smoke-free zone signage and indications of smoking in the outdoor areas of hospital campuses. Results: The overall median particulate matter < 2.5 μm concentration fell from 12.22μg/m3 (7.80-19.76μg/m3) in 2009 to 7.80μg/m3 (4.68-11.96μg/m3) in 2011. The smoke-free zone signage within the campus was moderately implemented after the legislation in most hospitals, and 55% of hospitals exhibited no indications of tobacco consumption around the grounds. Conclusions: After the law, particulate matter < 2.5 μm concentrations were much below the values obtained before the law and below the annual guideline value recommended by the World Health Organization for outdoor settings (10μg/m3). Our data showed the feasibility of implementing a smoke-free campus ban and its positive effects.