BACKGROUND: The influence of age at diagnosis in non-small cell lung cancer (NSCLC) prognosis is unclear. OBJECTIVES: To compare in a Brazilian cohort of NSCLC patients of different age groups: 1) The overall survival; 2) Clinical features and treatment options. METHODS: This is a retrospective cohort study using a hospital-based registry, for NSCLC patients registered in years 2000-2009. Patients were grouped into three age groups: Young adults (YA: < 40 years), middle-aged (MA: 40-64 years) and elderly (E: ≥ 65 years). Kaplan-Meier was used to estimate overall survival and Cox regression for hazard ratios (HRs) and 95% confidence intervals. RESULTS: 17,422 NSCLC patients were included: 370 YA (2.1%), 8,697 MA (49.9%) and 8,355 E (48.0%). Compared with older age groups, the YA group had a higher proportion of females, patients diagnosed with adenocarcinoma and metastatic disease (63.2%). Overall survival was longer in YA in the entire cohort and in all clinical stages (CSs) (p < 0.001). For YA, higher education level was a good prognosis factor (compared with illiterate and incomplete elementary); advanced or metastatic disease (compared with early-stage disease) and treatment based in radiotherapy or chemotherapy (CT) (without surgery), compared with treatment combinations with surgery, were poor prognostic factors. Young men (but not women) had lower HR of death compared with older groups; YA had lower HR of death in all CSs compared with patients from older groups. A higher percentage of YA were treated with surgery or CT in early-stage disease compared with older groups. Besides that, YA and MA patients treated with surgery or CT had a better prognosis than elderlies. Conclusions: In this Brazilian cohort of NSCLC patients, most young individuals were diagnosed with metastatic disease. YA presented longer survival than older age groups in all CSs, but mainly in CS I/II and III, where some patients may achieve long remissions or cure.