BACKGROUND: Coexisting disease constitutes a challenge for the provision of optimal cancer care. The influence of comorbidity on lung cancer management and prognosis remains incompletely understood. We assessed the influence of comorbidity on treatment intensity and prognosis in a population-based setting in patients with nonsmall cell lung cancer. MATERIAL AND METHODS: Our study was based on information available in Lung Cancer Data Base Sweden (LcBaSe), a database generated by record linkage between the National Lung Cancer Register (NLCR) and several other population-based registers in Sweden. The NLCR includes data on clinical characteristics on 95% of all patients with lung cancer in Sweden since 2002. Comorbidity was assessed using the Charlson Comorbidity Index. Logistic regression and time to event analysis was used to address the association between comorbidity and treatment and prognosis. RESULTS: In adjusted analyses encompassing 19,587 patients with a NSCLC diagnosis and WHO Performance Status 0-2 between 2002 and 2011, those with stage-IA-IIB disease and severe comorbidity were less likely to be offered surgery (OR: 0.45; 95% CI: 0.36-0.57). In late-stage disease (IIIB-IV), severe comorbidity was also associated with lower chemotherapy treatment intensity (OR: 0.76; 95% CI: 0.65-0.89). In patients with early, but not late-stage disease, severe comorbidity in adjusted analyses was associated with an increased all-cause mortality, while lung cancer-specific mortality was largely unaffected by comorbidity burden. CONCLUSIONS: Comorbidity contributes to the poor prognosis in NSCLC patients. Routinely published lung cancer survival statistics not considering coexisting disease conveys a too pessimistic picture of prognosis. Optimized management of comorbid conditions pre- and post-NSCLC-specific treatment is likely to improve outcomes.