Given the high short-term risk of stroke after transient ischemic attack, we hypothesized that substantial acute neurological recovery in patients presenting with cerebral ischemia would be associated with a greater risk of subsequent neurological deterioration due to recurrent cerebral ischemia. Data from the Trial of ORG10172 in Acute Stroke Treatment, a randomized trial of the heparinoid danaparoid, were analyzed to determine whether substantial acute recovery, defined as an improvement of greater than or equal to 75% on National Institutes of Health Stroke Scale (NIHSS) between baseline and 24 hours, was associated with a greater risk of subsequent deterioration, defined as a worsening on the NIHSS between day 1 and day 90. Of 1,184 subjects meeting entry criteria, 63 (5.3%) had substantial acute recovery. Subsequent deterioration was more common in those with substantial acute recovery compared with others (48 vs 33%; p = 0.028 by Fisher's exact test). In multivariable models, substantial acute recovery remained an independent predictor of subsequent deterioration (odds ratio, 3.0; 95% confidence interval, 1.7-5.2; p < 0.001). Among patients with acute cerebral ischemia, those who recover substantially within 24 hours may be at greater risk of subsequent neurological deterioration due to causes other than hemorrhage.