In order to evaluate the clinical and prognostic significance of early hyperfibrinogenemia in patients with transient ischemic attack (TIA) and ischemic cerebral infarction (ICI), we analyzed the relationships between plasma fibrinogen, brain damage severity, clinical status on admission and intra-hospital mortality. Vascular damage severity was estimated by measuring the necrotic area by computed axial tomography (CT) and indirectly by means of changes in some plasma enzymes (CK, LDH, GPT/ALT, and GOT/AST). Plasma fibrinogen levels were statistically higher in ICI than in TIA and control subjects (p < 0.0005; analysis of variance). Moreover, plasma fibrinogen was directly related to the extension of the necrotic area at CT scan (p < 0.05) and in ICI patients was positively correlated with CK (r = 0.50, p < 0.01), LDH (r = 0.41, p < 0.05) and GOT/AST (r = 0.42, p < 0.05) serum levels, but not with GPT/ALT. A higher plasma fibrinogen value was observed in patients with stupor or coma compared with those with alert consciousness (p < 0.05). In patients who died during hospitalization, fibrinogen levels were higher than those of subjects who were discharged (p < 0.005). The results indicate that in the early phase of cerebral ischemia, plasma fibrinogen levels are related to the severity of the clinical status and to the extension of the brain vascular damage, thus representing a negative clinical and prognostic factor of the disease.