A 63-year-old man who diagnosed with lung cancer had worked for 13.5 years (1999–2013) as a spray painter. The Occupational Lung Diseases Institute conducted retrospective exposure assessment to examine whether a spray painter job he had performed could be associated with the development of lung cancer. We investigated lung cancer carcinogens in his work environment. The safety data sheet of six powder coating products showed that powder coatings contained 1–10% of hexavalent chromium. In addition, our quantitative analysis of powder coating samples also showed that the hexavalent chromium contents quantified in the yellow-green and red powder coating samples were 0.27% and 0.95%, respectively. In order to estimate his exposure level of hexavalent chromium, we measured a personal exposure level of hexavalent chromium for a spray painter in accordance with the National Institute for Occupational Safety and Health #7605 method. The results showed that the spray painter was exposed to the high level of hexavalent chromium (216.9 µg m–3). Furthermore, we estimated that he was likely exposed to several lung cancer carcinogens such as crystalline silica or asbestos over the approximately 24 years at various construction sites prior to assuming a job as a spray painter. Therefore, we concluded that his lung cancer was caused by substantial exposure to several lung cancer carcinogens over approximately 37.5 years. Particularly, exposure characteristic to hexavalent chromium could substantially contribute to the development of lung cancer, despite of the sole case of exposure assessment.