Introduction Monitoring the activities and impacts of tobacco industries is vital for tobacco control. Based on tobacco industry financial statements and a nationally representative survey of Korean adolescents, we examined the association between tobacco industry commercial advertising expenses and advertising exposure among Korean adolescents.Methods The commercial advertising expenses of three major tobacco industries in Korea (KT&G, Philip Morris Korea, and British and American Tobacco Korea) were identified in a repository (Data Analysis Retrieval and Transfer System) established by the Korean Financial Supervisory Service. The yearly advertising expenses were merged with data from the Korean Youth Risk Behavior Survey (2015–2018 and 2021, total N=309 190). We used logistic regression analyses to analyse the associations between tobacco industry advertising expenses and adolescent tobacco advertisement exposure.Results In 2021, the total advertising expenses of the three companies exceeded US$260 million, and the proportion of Korean adolescents exposed to tobacco advertisements ranged from 65.9% to 78.7% during 2015–2018 and 2021. Higher advertising expense sizes were associated with the risk of exposure to tobacco advertisements in both girls and boys, with OR of 1.009 (95% CI (1): 1.008 to 1.010) and 1.010 (95% CI: 1.009 to 1.011), respectively.Conclusion Tobacco industry advertising expenses are associated with tobacco marketing exposure among adolescents. We used financial data to identify the reach of tobacco advertising among Korean adolescents. It is essential to increase tobacco industry surveillance using various data sources and to regulate tobacco advertising more strongly.