Background Serum fibrin-monomer (FM) is a precursor of stable fibrin, and is a sensitive marker of a systemic hypercoagulable state. It has been reported that, in patients with acute ischemic stroke, higher levels of serum FM reflect intracardiac thrombus formation. Methods and Results Serum coagulation and fibrinolytic activity were measured in 113 patients with acute ischemic stroke within 7 (6±1) days after onset. The patients were followed for a mean of 354 (range 36-585) days. The primary endpoints were ischemic stroke recurrence with/without death. FM was markedly higher in the 19 cases with stroke recurrence (49.6±53.6 μg/ml) than in the 94 patients without stroke recurrence (14.6±30.5 μg/ml; p=0.008). The cerebrovascular event rates were markedly higher in the 12 cases with FM ≥16.5 μg/ml (37.5%) than in the 7 cases with FM <16.5 μg/ml (8.6%; p<0.001). Cox proportional hazards multivariate analysis showed that the FM level was an independent predictor of ischemic stroke recurrence with/without death (hazard ratio, 1.516 per + 1 standard deviation increase; 95% confidence interval, 1.042-2.180; p=0.036). Conclusions Elevated serum FM levels in hospitalized ischemic stroke patients may be associated with a persistent systemic hypercoagulable state and high long-term rates of cerebrovascular events. (Circ J 2007; 71: 1573 - 1579)