Some previous studies have reported that 80% of cancer patients take multivitamin and/or mineral supplements. The consequences of such self-directed supplementation have not been examined previously in non-small-cell lung cancer (NSCLC) patients. The goal of this study was to determine whether or not vitamin/mineral supplementation is associated with improved survival and quality of life in a cohort of NSCLC patients. NSCLC patients or their proxies who responded to a questionnaire on vitamin/mineral use were assessed for survival and quality of life. A total of 1129 patients or their proxies responded to a vitamin/mineral questionnaire. Seven hundred and fourteen were vitamin/mineral users of either multivitamins or other specific vitamin/mineral supplements, and the rest were non-users. Median survival was 4.3 years vs. 2.0 years for vitamin/mineral users and non-users, respectively. A Cox proportional hazards model showed a relative risk of death of 0.54 (95% CI 0.44 to 0.65) (P < 0.01) in favour of vitamin/mineral use after adjustment for multiple prognostic factors, including tumour stage. The Lung Cancer Symptom Scale showed better quality of life among vitamin/mineral users, mean difference in score of 3 (95% CI 0.8 to 5.1) (P < 0.01), and after adjusting for related variables there remained a trend in favour of vitamin/mineral use, mean difference 1.8 (95% CI 0.2 to 3.9) (P=0.08).