Introduction: Lung cancer is the leading cause of cancer mortality worldwide. We analyzed changes in treatment and their potential effect on survival of non-small cell lung cancer (NSCLC) patients in the Netherlands. Methods: All NSCLC patients diagnosed during 1989–2009 (n=147,760) were selected from the population-based Netherlands Cancer Registry. Differences in treatment over time were tested by the Cochran-Armitage trend test. The effects of sex, age, histology, and treatment on relative survival were estimated in multivariable models. Follow-up was completed until January 1, 2010. Results: Between 1989 and 2009, the proportion of younger patients (younger than 75 years) with stage I undergoing surgery increased from 84 to 89% and among elderly (75 years or elder) from 35 to 49%; for stage II, this proportion decreased from 80 to 70% and remained about 25% in respectively younger and older patients. Adjuvant chemotherapy for stage II increased to from 0 to 24% in younger patients but remained less than 5% among the elderly. Chemoradiation increased from 8 to 43% among younger patients with stage III and from 1 to 13% among elderly. In stage IV, chemotherapy in younger patients increased from 10 to 54% and in elderly from 5 to 21%. Five-year relative survival of the total group increased from 14.8 to 17% (especially among females, younger patients, and within each stage), which could be partly explained by changes in treatment and better staging. Conclusions: Over a 20-year period, application of therapy, which is currently considered as standard, has improved. This resulted in small improvements in survival within all stages.