C1-inhibitor (C1-INH) is a major regulator of the complement classical pathway. Besides this action, it may also inhibit other related inflammatory systems. We have studied the effect of C1-INH in C57BL/6 mice with focal transient brain ischemia induced by 30 minutes of occlusion of the middle cerebral artery. C1-INH induced a dose-dependent reduction of ischemic volume that, with the dose of 15 U/mouse, reached 10.8% of the volume of saline-treated mice. Four days after ischemia the treated mice had significantly lower general and focal neurological deficit scores. Fluoro-Jade staining, a marker for neuronal degeneration, showed that C1-INH-treated mice had a lower number of degenerating cells. Leukocyte infiltration, as assessed by CD45 immunostaining, was also markedly decreased. We then investigated the response to ischemia in C1q(-/-) mice. There was a slight, nonsignificant decrease in infarct volume in C1q(-/-) mice (reduction to 72.3%) compared to wild types. Administration of C1-INH to these mice was still able to reduce the ischemic volume to 31.4%. The study shows that C1-INH has a strong neuroprotective effect on brain ischemia/reperfusion injury and that its action is independent from C1q-mediated activation of classical pathway.