Objective To examine if there were changes in the proportions of hardcore smokers and its associated factors before and after the implementation of a smoking-free legislation and warning labels on cigarette package in Hong Kong in January 2007. Study Design Repeated cross-sectional surveys of the general population in Hong Kong. Methods We used data from all the daily smokers aged 15 or above in the population-based surveys, Thematic Household Surveys, carried out in 2005 (N=3,740) and 2008 (N=2,958) to estimate the prevalence of hardcore smokers before and after the implementation of the legislation. Logistic regression model was used to identify the factors associated with hardcore smoking and to examine if there is any change in their associations with the likelihood of hardcore smoking after the legislation. Results The proportion of hardcore smokers among current daily smokers increased from 22.5% (95%CI 21.1% to 23.8%) in 2005 to 28.3% (95%CI 26.7% to 29.9%) in 2008. There were changes in the magnitudes of the associations of hardcore smoking with three factors: 'Necessity in social functions' (OR = 0.54, 95%CI 0.31 to 0.95) and 'Necessity for killing time' (OR = 0.56, 95%CI 0.36 to 0.89) decreased while that with 'Necessity as refreshment' increased (OR = 3.02, 95%CI 1.43 to 6.39) after the smoking ban and warning labels. In addition, 'Smoking had become a habit' was the strongest factor associated with hardcore smoking (OR = 4.88, 95%CI 4.02 to 5.93). Conclusions The proportion of hardcore smokers remained stable in Hong Kong from 2005 to 2008. While the implementation of the two tobacco control measures might have provided an environment to reduce social smoking in hardcore smokers, addiction appeared to be the most important associated factor of hardcore smoking. More effective and tailor-made cessation services that target this group of smokers are needed.