Matrix metalloproteinases (MMP) constitute an endopeptidase family involved in various physiological and pathological processes. It was demonstrated that plasma MMP-9 level was increased in patients with acute ischemic stroke. In this study, it was investigated whether there was a relationship between the levels of plasma MMP-9 and the severity of stroke and infarct volume in patients with acute ischemic stroke. A total of 32 patients with acute ischemic stroke, (16 males and 16 females) and 30 healthy controls were included in the study. Plasma MMP-9 levels were measured using ELISA method. Computed tomography was performed at 48th hour and infarct volume was calculated using the Cavalieri method. The National Institute of Health Stroke Scale (NIHSS) was checked at baseline, 12, 24, and 48th hour. Plasma MMP-9 levels of the patient group at baseline, 12, 24, and 48th hour were found significantly higher compared to the control group (p < 0. 05). An important correlation between MMP-9 levels and the infarct volume was observed at baseline, 12, 24, and 48th hour (p < 0. 001). Furthermore, a positive correlation was recorded between plasma MMP-9 levels and NIHSS scores at baseline, 12, 24, and 48th hour (p < 0. 001). Plasma MMP-9 levels of those of suffering medium and heavy damages were found significantly higher when compared to those of having slight damage (p < 0. 05). A significant relationship was also observed between infarct volumes and neurological deficits (p < 0. 05). Plasma MMP-9 levels of the patients at 48th hour were found to be significantly lower in recovered patients compared to those who did not improved or worsened (p < 0. 05). A positive correlation was recorded between the infarct volume and infarct progression (p < 0. 05). In conclusion, this study showed that plasma MMP-9 level substantially increased during the acute period of ischemic cerebrovascular disease and correlated with the severity of the disease and infarct volume. The definition of the exact role of plasma MMP-9 after ischemic stroke will have important diagnostic implications for stroke and for the development of therapeutic strategies aimed at modulating plasma MMP-9. © 2012 Belgian Neurological Society.