© 2015 Elsevier Ltd. Abstract Background Adjuvant chemotherapy (ACT) in non-small-cell lung cancer (NSCLC) improves overall survival, but the benefits must be weighed against its harms. We sought to determine the survival benefits that patients and their doctors judged sufficient to make ACT in NSCLC worthwhile. Methods 122 patients completed a self-administered questionnaire at baseline and 6 months (before & after ACT, if they had it); 82 doctors completed the questionnaire once only. The time trade-off method was used to determine the minimum survival benefits judged sufficient in four hypothetical scenarios. Baseline survival times were 3 years & 5 years and baseline survival rates (at 5 years) were 50% & 65%. Results At baseline, the median benefits judged sufficient by patients were an extra 9 months (Interquartile range (IQR) 1-12 months) beyond 3 years & 5 years and an extra 5% (IQR 0.1-10%) beyond 50% & 65%. At 6 months (n = 91), patients' preferences had the same median benefit (9 months & 5%) but varied more (IQRs 0-18 months & 0-15%) than at baseline. Factors associated with judging smaller benefits sufficient were deciding to have ACT (P = 0.01, 0.02) and better well-being (P = 0.01, 0.006) during ACT. Doctors' preferences, compared with patients' preferences, had similar median benefits (9 months & 5%) but varied less (IQR 6-12 months versus 1-12 months, P <0.001; 5%-10% versus 0.1-10%, P <0.001). Conclusion Most patients and doctors judged moderate survival benefits sufficient to make ACT in NSCLC worthwhile, but the preferences of doctors varied less than those of patients. Doctors should endeavour to elicit patients' preferences during discussions about ACT in NSCLC.