Background: We hypothesized that fibrinogen, as a marker of chronic inflammation, is inversely associated with forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV 1) in healthy persons. Methods: The CARDIA cohort started in 1985 and included black and white men and women, aged 18-30, from the general population. Spirometry testing conducted at years 5 and 10 [FVC, FEV 1, and their ratio (FEV 1 /FVC)] was studied relative to plasma fibrinogen levels measured at year 5 (cross-sectional n = 4040) and at year 7 (longitudinal n = 3001), controlling for race, sex, age, height, smoking, asthma, body mass index, physical activity, birth control pill use, and alcohol intake. Results: In cross-sectional analyses, FVC at year 5 was lower by 166 ml (95% confidence interval 116-216 ml) in the highest vs lowest year 5 fibrinogen quartile. At year 10, holding year 5 FVC and change in fibrinogen (year 7-year 5) constant, the difference in FVC between the highest and the lowest year 5 fibrinogen quartiles widened by 67 ml (95% CI 31-103 ml). The corresponding differences for FEV 1 were 166 ml (95% CI 146-253 ml) at year 5 and 45 ml (95% CI 11-80 ml) widening by year 10. The FEV 1 /FVC ratio was unrelated to plasma fibrinogen. Conclusion: These findings are consistent with the hypothesis that fibrinogen, possibly as a marker for chronic low-grade inflammation, is associated with modest deterioration of lung function in healthy young adults. © 2006 Oxford University Press.