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Background: The gold standard endpoint in clinical trials of adjuvant chemotherapy (CT) in lung cancer is overall survival (OS), which while a reliant and simple-to-measure outcome, takes a long time to observe in this setting. This study aimed to evaluate disease-free survival (DFS) as a potential surrogate endpoint for OS in adjuvant CT trials, which could lead to more rapid conclusion of trials. Methods: This analysis was based on individual patient data of 7,626 patients (pts) and 25 randomized trials from two large meta-analyses of adjuvant CT: surgery alone versus surgery  CT and surgery  radiotherapy (RT) versus surgery  RT  CT. DFS was defined as the time from randomization to the first event (local or distant recurrence or death from any cause). A correlation approach was used to assess individual and trial level surrogacy: at the individual level, to estimate association between distributions of DFS and OS (), and at trial level, to estimate association between treatment effects on DFS and OS (R). Values of  and R closer to 1.0 would indicate strong surrogacy. Results: Analysis 1 (without RT) included 18 trials (5,379 pts, 2,525 DFS events and 2,163 deaths); analysis 2 (with RT) included 7 trials (2,247 pts, 1,673 DFS events and 1,566 deaths). 79% and 84% of DFS events, respectively, occurred in the first three years. Correlations between DFS and OS were very strong, both at the individual (0.91 in trials without RT and 0.93 in trials with RT) and trial level (R0.96, 95% confidence interval [0.92-1.00] and 0.99 [0.98-1.00], respectively). Considering only events occurring in the first three years and deaths in the first five years, trial-level correlation remained strong (R0.94 [0.88-1.00] and 0.98 [0.95-1.01] respectively). Conclusions: Our large database provides good evidence that disease-free survival is a valid surrogate endpoint for overall survival in operable non-small cell lung cancer in the adjuvant CT setting. Supported by French Cancer League, PHRC and British Medical Research Council.