Neuroserpin is a brain-derived natural inhibitor of tissue plasminogen activator (tPA) that has shown neuroprotective effects in animal models of brain ischaemia. Our aim was to investigate the association of neuroserpin levels in blood with functional outcome in patients with acute ischaemic stroke. Due to the potential effect of tPA treatment interfering on neuroserpin levels, we studied two different cohorts: 129 patients not treated with tPA and 80 patients treated with intravenous tPA within 3 hours (h) from symptoms onset. Neuroserpin levels were measured by ELISA. Good functional outcome at three months was defined as Rankin scale score ≤2. In the two cohorts, serum neuroserpin levels on admission were significantly higher than at 24 h, 72 h and in healthy subjects. In non tPA-treated patients, neuroserpin levels decrease at 24 h, but not levels at baseline, were associated with good outcome (for each quartile decrease, adjusted odds ratio [OR] 15.0; 95% confidence interval [CI], 3.5 to 66). In the tPA-treated cohort, high neuroserpin levels before tPA bolus had the stronger effect on favourable outcome (for each quartile, OR 13.5; 95%CI, 3.9 to 47). Furthermore, for each quartile in neuroserpin levels before tPA bolus there was a 80% (95%CI, 48 to 92) reduction in the probability of subsequent parenchymal haematoma. In summary, high serum neuroserpin levels before intravenous tPA and neuroserpin levels decrease at 24 h after ischaemic stroke, independently of tPA treatment, are associated with good functional outcome. These findings support the concept that neuroserpin might play an important role during cerebral ischaemia.