Objective To describe the approval process and implementation of the 100% smokefree law in Mexico City and a competing federal law between 2007 and 2010.

Methods Reviewed smokefree legislation, published newspaper articles and interviewed key informants.

Results Strong efforts by tobacco control advocacy groups and key policymakers in Mexico City in 2008 prompted the approval of a 100% smokefree law following the WHO FCTC. As elsewhere, the tobacco industry utilised the hospitality sector to block smokefree legislation, challenged the City law before the Supreme Court and promoted the passage of a federal law that required designated smoking areas. These tactics disrupted implementation of the City law by causing confusion over which law applied in Mexico City. Despite interference, the City law increased public support for 100% smokefree policies and decreased the social acceptability of smoking. In September 2009, the Supreme Court ruled in favour of the City law, giving it the authority to go beyond the federal law to protect the fundamental right of health for all citizens.

Conclusions Early education and enforcement efforts by tobacco control advocates promoted the City law in 2008 but advocates should still anticipate continuing opposition from the tobacco industry, which will require continued pressure on the government. Advocates should utilise the Supreme Court's ruling to promote 100% smokefree policies outside Mexico City. Strong advocacy for the City law could be used as a model of success throughout Mexico and other Latin American countries.