Background Previous studies showed reduction of hospital admissions for asthma after implementation of comprehensive smoke-free legislation. We aimed to evaluate the impact of comprehensive smoke-free legislation implemented in Hong Kong in 2007 on hospital admissions for childhood lower respiratory tract infection (LRTI).

Methods We obtained data on 75 870 hospital admissions for LRTI among children ≤18 years of age between January 2004 and December 2012 from all Hospital Authority hospitals. Using a negative binomial regression model, we assessed the impact of smoke-free legislation on admission counts.

Results After legislation implementation, there was an immediate effect with a change in the admission count of −33.5% (95% CI −36.4% to −30.5%), and a change in time trend to −13.9% per year (95% CI −16.0% to −11.7%). Overall, the legislation was associated with a net 47.4% reduction in admission counts in the first year. We estimated that the legislation was associated with a reduction of 13 635 admissions in the first 6 years after implementation. The immediate reduction and change in time trend was more apparent among school-age than preschool children.

Conclusions Implementation of comprehensive smoke-free legislation was associated with a significant reduction in hospital admissions for childhood LRTI.