<b><i>Background:</i></b> Up-to-date oncological therapy has been accomplished through the results of clinical trials (CTs). We analyzed the overall survival (OS) of patients with non-small cell lung cancer (NSCLC) and its relation to CT enrollment. <b><i>Methods:</i></b> The study included 1,042 patients with advanced NSCLC treated at the Instituto Nacional de Cancerología. All patients received treatment according to the national and international guidelines. Data were collected from medical records. Patients were subgrouped on the basis of their CT enrollment as follows: participants in any CT (ACT), exclusively intervention CTs (ICT) or exclusively pharmaceutical-sponsored CTs (PCT). <b><i>Results:</i></b> The CT enrollment effect was assessed through a multivariate Cox proportional hazards model. Thirty percent of the patients were in ACT, 28.3% in ICT and 13.7% in PCT. Female gender (p = 0.001), adenocarcinoma histology (p = 0.018), positive EGFR mutation (p = 0.006), and better ECOG performance status (<2) (p ≤ 0.0001) were more frequent in patients enrolled in CT; further, tobacco smoking (p ≤ 0.0001) and KRAS mutation (p = 0.001) were more frequent in patients who were not enrolled in a CT. <b><i>Conclusion:</i></b> Enrollment in ACT was associated with a better OS (hazard ratio: 0.47-0.74). NSCLC patients enrolled in a CT have an improved survival in an independent manner to other prognostic factors.