OBJECTIVES: To assess the direct medical costs paid by patients for the treatments of key smoking-related diseases including lung cancer, chronic obstructive pulmonary disease, and coronary heart disease METHODS: A prevalence-based, disease-specific approach was employed. Three major smoking-related diseases- lung cancer, chronic obstructive pulmonary disease (COPD), and coronary heart disease (CHD) - were included in the analysis. Epidemiological and cost parameters were obtained from literatures. RESULTS: The number of cases attributable to smoking in year 2006 was 5,299 for lung cancer, 624,309 for COPD, and 52,605 for CHD. The highest out-of-pocket spending was for treatment of COPD (BAHT7,714,88 million) followed by CHD (BAHT1,773,65 million) and lung cancer (BAHT368.49 million). Total smoking-attributable out-of-pocket medical costs in 2006 amounted to BAHT9,857.02 million or 0.48% of GDP. CONCLUSIONS:The prevalence-based, disease specific analysis illustrated here shows that the health consequences and economic burden of smoking in Thailand are substantial. These impacts could be reduced by implementing national smoking-cessation and related tobacco-control policies of the types proven effective in reducing the prevalence of smoking in other countries.