Abstract--Elevated plasma fibrinogen is implicated in cardiovascular disease. However, it is not clear whether fibrinogen levels predict the development of hypertension. We examined the relationship between plasma fibrinogen level and hypertension in a population-based cohort study of 3654 participants (mean age: 61.5 years; range: 49 to 84 years) at the baseline examination (1992-1994) in the Blue Mountains region, west of Sydney, Australia, who were examined 5 years (1997-1999) later. Main outcomes of interest were prevalent hypertension (systolic blood pressure 140 mm Hg, diastolic blood pressure 90 mm Hg, or a combination of self-reported hypertension diagnosis and use of antihypertensive medications) at baseline (n=2212/3180) and 5-year incidence of hypertension among baseline normotensive individuals (n=361/637). Elevated plasma fibrinogen level was positively associated with prevalent hypertension both among men and women and positively associated with 5-year incident hypertension among men, independent of several cardiovascular risk factors. Multivariable odds ratio (95% CI) of 5-year incident hypertension comparing tertile 3 of plasma fibrinogen (3.9 g/L) with tertile 1 (3.2 g/L) was 1.95 (1.03 to 3.68; P trend=0.040). This prospective association, however, was not observed in women (odds ratio; 95% CI) comparing tertile 3 versus tertile 1 of plasma fibrinogen (1.00; 0.54 to 1.86; P trend=0.986). Subgroup analyses stratified by smoking, body mass index, diabetes, and blood pressure categories supported this male gender-specific pattern of association. These data provide prospective epidemiological evidence of an essential link between plasma fibrinogen level and incident hypertension among men but not among women, a finding consistent with that observed in the Atherosclerosis Risk in Communities Study.