The aim of our study was to show how the progression and severity of Familial Mediterranean Fever (FMF) is affected by procoagulant activity and alterations in the markers of thrombosis and fibrinolysis. The study cohort comprised 64 FMF patients who were classified as attack-free patients (Group 1; n=34 patients, aged 3-19 years) and attack patients (Group 2; n = 30 patients, aged 3-21 years). All patients were on colchicine treatment with the exception the newly diagnosed patients in Group 2. A total of 14 healthy subjects between 5-12 years of age were enrolled as controls (Group 3). Laboratory tests, including leukocyte and thrombocyte counts, erythrocyte sedimentation rate, CRP, fibrinogen, PT, aPTT, Factor VIII, vW factor, D-dimer, P-selectin, tPA and PAI-1, were carried out on all patients. Inflammation continued both during the attack and attack-free period in FMF. The prolongation of PT was observed during attacks (PT=13.6 s in Group 2, and PT=12.6 s in Group 3; p=0.002). tPA levels increased in FMF patients (tPA levels of group 1, 2 and 3 were 12.6, 13.2 and 9.7 ng/ml, respectively; p=0.01). P-selectin was lower in both patient groups than in the control group. During attack periods PAI-1 levels increased (PAI-1 level of Group 1: 89.6 ng/ml and PAI-1 level of Group 2: 335.7 ng/ml, p=0.000). Inflammation with increased acute phase reactants continued during both attack and attack-free periods in FMF patients. Prolongation of PT and differences in tPA and P-selectin levels suggest that hypercoagulability may have a role in the etiopathogenesis of FMF. It may be possible to use PAI-1 as a marker for the attacks of FMF.