ABSTRACT Objectives: Many different factors affect the transferability of cost-effectiveness results between countries. The objective is to quantify the impact of nine potential causes of variation in cost-effectiveness of pharmacological smoking cessation therapies (SCTs) between The Netherlands (reference case), Germany, Sweden, UK, Belgium, and France. Methods: The life-time benefits of smoking cessation were calculated using the Benefits of Smoking Cessation on Outcomes model, following a cohort of smokers making an unaided quit attempt, or using nicotine replacement therapy (NRT), bupropion, or varenicline. We investigated the impact of between-country differences in nine factors-demography, smoking prevalence, mortality, epidemiology and costs of smoking-related diseases, resource use and unit costs of SCTs, utility weights and discount rates-on the incremental net monetary benefit (INMB), using a willingness-to-pay (WTP) of euro 20,000 per quality adjusted life year (QALY). Results: The INMB of 1000 quit attempts with NRT versus unaided, varies from euro 0.39 million (Germany) to euro 1.47 million (France). The differences between the countries were primarily due to differences in discount rates, causing the INMB to change between -65% to +62%, incidence and mortality rates (epidemiology) of smoking-related diseases (-43% to +35%) and utility weights. Impact also depended on the WTP for a QALY and time horizon: at a low WTP or a short time horizon, the resource use and unit costs of SCTs had the highest impact on INMB. Conclusions: Although all INMBs were positive, there were significant differences across countries. These were primarily related to choice of discount rate and epidemiology of diseases.