Plasma fibrinogen is a strong predictor of ischaemic arterial disease in women. Sex steroid hormones including hormone therapy may play an important role in the development of cardiovascular disease. However, whether endogenous sex steroid hormones influence the plasma fibrinogen concentrations among postmenopausal women remains unclear. To investigate the association of plasma fibrinogen levels with endogenous sex steroid hormones and sex hormone binding globulin (SHBG) among postmenopausal women. We used data from the French prospective Three-City cohort study that included 9294 noninstitutionalized men and women over 65 years of age. Total 17β-oestradiol (E2, pg/ml), total testosterone (T, ng/ml), SHBG (nm) and fibrinogen (g/l) were measured in stored plasmas in a subcohort of 602 randomly selected postmenopausal women who used neither hormone medication nor anticoagulation therapy. Multivariate linear regression models were used to estimate the regression coefficients assessed in fibrinogen unit by 1 SD increase in log-distribution of sex steroid hormones and SHBG. E2 but neither T nor SHBG was positively associated with plasma fibrinogen levels (β = 0·148, P < 0·001). Adjustment for cardiovascular risk factors including diabetes made no substantial change to the results (β = 0·145, P < 0·001). The association of fibrinogen with E2 was stronger among women with body mass index over 25 kg/m(2) compared with those with normal weight (β = 0·156, P < 0·001 and β = 0·092, P = 0·02, respectively, P for interaction = 0·04). E2 emerges as a positive and independent correlate of plasma fibrinogen among postmenopausal women, especially in subjects who are overweight. These findings suggest a deleterious effect of endogenous oestrogens on cardiovascular risk profile among postmenopausal women.