Background/Objectives:B vitamins and related enzymes involved in one-carbon metabolism are necessary for DNA replication, DNA repair and regulation of gene expression. Disruption of one-carbon mechanism may affect cancer risk. We investigated prospectively the relationship between dietary intakes of methionine, B vitamins associated with one-carbon metabolism and risk of lung cancer.Subjects/Methods:The Melbourne Collaborative Cohort Study recruited 41 514 men and women aged 40-69 years between 1990 and 1994. During follow-up of 14 595 men and 22 451 women for an average of 15 years, we ascertained 348 incident lung cancers. Dietary intake of B vitamins and methionine was estimated from a 121-item food frequency questionnaire. Hazard ratios (HR) and 95 confidence intervals (CI) were estimated using Cox regression.Results:In current smokers, dietary intake of riboflavin was inversely associated with lung cancer risk (HR=0.53; 95 CI: 0.29-0.94, fifth versus first quintile; P-linear trend=0.01). No associations were found for former or never smokers or for dietary intake of any of the other B vitamins or methionine.Conclusion:Overall, we found little evidence of an association between B vitamins or methionine and lung cancer risk. The weak inverse association between riboflavin and lung cancer risk in current smokers needs further investigation.