BACKGROUND: Progressing stroke (PS) variably develops from initially the same size and severity, and is most frequently observed in lacunar infarctions. We investigated fractional anisotrophy (FA), mean diffusivity (MD) and infarct volume by using diffusion tensor imaging during the acute phase of ischemic stroke to determine whether these parameters are useful in characterizing and predicting PS. METHODS: In this study, 55 consecutive patients admitted within 24 hours of the onset of their first ischemic stroke were included. NIH stroke scale (NIHSS) and Canadian Neurological scale (CNS) were performed upon admission, twice a day, and at discharge. Modified Rankin scale and Barthel index were also evaluated. PS was defined as a 2-point drop in NIHSS and a 1-point drop in CNS from admission to day 3. A correlation analysis was performed between clinical scale scores and imaging parameters, and the distribution of those values was compared between the two groups with and without PS. RESULTS: Significant correlations were observed between clinical scale scores and infarct volumes. The FA ratio in 14 patients with PS was lower than the patients without PS (p=0.004). Other characteristics including infarct volume and MD ratio were not different. The FA ratio remained as an independent predictor of PS (OR, 1.055; p=0.011). CONCLUSIONS: In acute ischemic stroke within the first 24 hours, only infarct volume was correlated with clinical status. However, patients with PS showed lower FA values, which accounts for rapid and severe vasogenic edema involving the disruption of the cell membrane and axonal fibers. Moreover, FA may be a predictor of PS.