In this study, the functional and clinical evolution of the cerebral postischemic hyperperfusion (CPH) were evaluated. METHODS Forty-four noncomatose patients suffering from unilateral cerebral ischemia located in the internal carotid territories were studied. Twenty-five consecutive patients having CPH with 133Xe-SPECT cerebral blood flow (CBF) measurement and 19 patients without cerebral hyperperfusion matched for age. CBF, vasoreactivity to acetazolamide and the evolution of the clinical state, scored by the National Institutes of Health scale for stroke, were compared. RESULTS CPH coincided with CT-scan abnormalities in 57% of cases. The mean cerebral vasoreactivity to acetazolamide was comparable in the two groups, but there was local vasoplegia in the hyperperfused areas in 20% of CPH patients, including two cases (8%) with a steal syndrome. Comparison of the initial and late clinical scores showed no significant difference between patients with and without CPH. For patients without CPH, the interhemispheric CBF asymmetry was correlated with the initial and the late scores (p < 0.0001, r = 0.81). For the CPH group, the interhemispheric asymmetry, compensated or even inverted by the hyperperfusion, was not correlated with the initial score (ns, p = 0.051, r = 0.42) and was weakly correlated to the late score (p = 0.048, r = 0.43). CONCLUSIONS The cerebral hemodynamics remain normal in 80% of cases of CPH patients. The presence of CPH does not interfere with the clinical evolution. The initial and late clinical scores were not different compared to those of patients without hyperperfusion. The clinical outcome of the CPH patients cannot be accurately predicted by the interhemispheric asymmetry.