Background Hong Kong has one of the lowest smoking prevalence both within China and among high-income economies. As tobacco use consistently declined over the past decades, we examine whether there are corresponding cost reductions.

Methods Data were sourced from diverse population-wide datasets including government reports and public hospital records. Costs were calculated using Global Burden of Disease (GBD) 2019 risk estimates for active smoking. Direct costs encompassed public and private healthcare expenses, while indirect costs included the value of years of productive life lost, days off work due to active smoking or secondhand smoke exposure, and long-term care costs.

Findings Active smoking accounted for 26.3% of deaths in people aged 35 or over. Healthcare costs amounted to US$342 million and US$45 million for active and secondhand smoking. Annual tobacco-related diseases reached US$1.27 billion (0.3% of 2021 Hong Kong GDP). Compared with previous methods, the analysis using GBD 2019 risk estimates showed a twofold increase in lives lost due to active smoking but a 31.0% decrease for secondhand smoking.

Interpretation Past studies greatly underestimate the health burden of tobacco compared with more recent data on the wider risks. Despite a decline in smoking prevalence, the total costs associated with smoking have risen as utilisation shifts from primary care towards more expensive specialist care. The long-term health and economic impacts of tobacco use remain substantial even in regions of China that have now achieved low smoking prevalence.