Impairment of cerebrovascular autoregulation may promote secondary brain injury in acute brain insults. Until now, only limited data are available on autoregulation in patients with spontaneous intracerebral hemorrhage. In the current study, we aimed to investigate cerebrovascular reactivity and its significance for outcome in spontaneous intracerebral hemorrhage. We continuously recorded mean arterial pressure, intracranial pressure, and cerebral perfusion pressure for mean 95 hours in 20 patients with spontaneous intracerebral hemorrhage. The moving correlation coefficient between mean arterial pressure and intracranial pressure (pressure reactivity index), an index of cerebral vasoreactivity, was calculated from the available artifact-free monitoring time (mean, 50.4 hours). In the univariate analysis pressure reactivity index (r=0.66; P=0.002), hemorrhage volume (r=0.62; P=0.007), cerebral perfusion pressure (r=-0.71; P=0.001), mean arterial pressure (r=-0.61; P=0.005), and hematoma growth (r=0.53; P=0.02) significantly correlated with National Institutes of Health Stroke Scale Score at discharge. In a multivariate stepwise linear regression model, pressure reactivity index remained the only independent predictor of outcome (beta=0.659; P=0.004). In the subgroup of patients with pressure reactivity index greater than a functional threshold of >0.2, the correlation between mean cerebral perfusion pressure and outcome remained significant (r=-0.73; P=0.0102), whereas National Institutes of Health Stroke Scale Score at discharge did not correlate with cerebral perfusion pressure in patients with pressure reactivity index <0.2 (r=-0.05; P=0.9078). We found evidence for impaired cerebral vasomotor activity as measured by pressure reactivity index in patients with spontaneous intracerebral hemorrhage. We suggest that impaired cerebrovascular reactivity contributes to poor outcome in intracerebral hemorrhage patients. This effect may be mediated by fluctuations in cerebral perfusion.