Background: Lung cancer affects older adults and is the leading solid tumor in terms of death. A Comprehensive Geriatric Assessment (CGA) is recommended before cancer treatment to guide therapy management. Patients and methods: This study was conducted between September 2015 and January 2019. During this period of time, all consecutive older outpatients referred for a CGA before initiation of lung or thoracic tumor treatment were included. The objectives were to describe the impact of geriatric factors on unplanned hospitalizations and overall survival (OS). The study was approved by a local ethics committee. Results: Overall, 228 patients were recruited. The median age was 78.7 ± 5 years. The majority (82%) of patients were diagnosed with non-small-cell lung cancer, and the most common (40.4%) treatment was systemic therapy. In multivariate analysis, factors associated with unplanned hospitalizations within the first 3 months were male gender (adjusted odds ratio [aOR], 3.3; 95% confidence interval [CI], 1.5-7.2), systemic therapy (aOR, 2.6; 95% CI, 1.1-6.2), and fall history (aOR, 3.6; 95% CI, 1.6-8.2). Factors associated with a decrease in OS in the multivariate Cox model analysis were male gender (hazard ratio [HR], 3.9; 95% CI, 2.1-7.3), stage IV (HR, 1.6; 95% CI, 1.0-2.6), G8 ≤ 14 (HR, 3.5; 95% CI, 1.1-11.4), systemic therapy (HR, 2.6; 95% CI, 1.2-5.5), Eastern Cooperative Oncology Group performance status ≥ 2 (HR, 2.0; 95% CI, 1.2-3.4), and impaired handgrip strength (HR, 1.6; 95% CI, 1.0-2.5). Conclusion: G8 score and handgrip strength are important to predict OS in older adults treated for thoracic tumors. In the CGA, fall history was associated with unplanned hospitalization.