Inherited thrombophilic conditions were evaluated in 28 patients with venous thrombosis at unusual sites (VTUS; 14 cerebral vein thromboses, 14 portal or hepatic vein thromboses) and compared with data from 177 patients with deep vein thrombosis of the lower limbs (DVT) and 280 controls. FII G20210A mutation was significantly more prevalent and associated to increased risk both in DVT (16.4% vs. 6.1%, p=0.0004, OR, 95%C.I. 3.0,1.5-6.0) and in VTUS (32.1%, p<0.00001; OR, 95%C.I. 7.3, 2.6-20.4) than in controls, whereas FV Leiden and natural anticoagulant deficiencies were significantly associated only to DVT. Although in VTUS a role for FII G20210A is shown, the contribution of inherited thrombophilia seems to be more limited than in DVT. Thrombophilic factors other than those presently known should be probably involved in the pathogenesis of these events.