Up to one-third of patients admitted to a hospital due to an ischemic stroke or a transient ischemic attack show clinical worsening of symptoms in the first hours to days after admission. We analyzed on the basis of a large patient group the frequency of minor or major worsening and the possible predictors for worsening. In the nationwide Austrian Stroke Unit Registry, 11616 patients with ischemic stroke or transient ischemic attack and a known NIHSS on admission and discharge from the stroke unit were recorded between March 2003 and February 2007. 363 (3.13%) of these patients showed a minor deterioration (NIHSS difference between admission and discharge 2 or 3 points) and 559 (4.81%) a major deterioration (NIHSS difference 4 or more points). In a logistic regression model, diabetes mellitus [OR (95%CI) 1.8 (1.3-2.4)], arterial hypertension [1.8 (1.2-2.8)], a cardiogen embolic event [1.6 (1.1-2.4)], and a large vessel disease [1.7 (1.2-2.6)] were independent predictors for a minor deterioration. Predictors for a major deterioration were a higher age [1.0 (1.0-1.1)], hypertension [1.4 (1.1-2.0)], diabetes mellitus [1.5 (1.2-1.9)], a higher NIHSS at admission [1.1 (1.0-1.1)], and a large vessel disease [1.8 (1.3-2.4)]. This underlines the importance of early diagnostic workup and risk evaluation in order to prevent also early deterioration by immediate initiation of dedicated therapeutic approaches.