Background Scientific guidelines recommend the National Institutes of Health Stroke Scale for ischemic stroke assessment. However, many nurses find "slim" National Institutes of Health Stroke Scale versions or the Glasgow Coma Scale easier to use. Objective To compare 3 "slim" versions of the National Institutes of Health Stroke Scale and the Glasgow Coma Scale with the full National Institutes of Health Stroke Scale. Methods Components of the full National Institutes of Health Stroke Scale and Glasgow Coma Scale were abstracted from records of consecutive stroke patients. Items were subtracted from the full National Institutes of Health Stroke Scale, with items contained in "slim" versions retained. False-negative rates for neurological disability were calculated for the "slim" versions and the Glasgow Coma Scale. Results Data were collected from 172 acute stroke patients (median [interquartile range] 6 [3-12] for National Institutes of Health Stroke Scale, 15 [12-15] for Glasgow Coma Scale): 143 (83%) were ischemic stroke patients (27% posterior circulation strokes) and 29 (17%) were intracerebral hemorrhage patients. The value of "slim" scales and the Glasgow Coma Scale declined in a stepwise manner as the full National Institutes of Health Stroke Scale decreased because of false-negative results despite the presence of a measurable disabling deficit. False-negative rates were 5% to 19% on "slim" versions and 56% with the Glasgow Coma Scale. Conclusions Use of "slim" scales, and in particular the Glasgow Coma Scale, substantially decreases the value of a structured neurological assessment, particularly in patients with low National Institutes of Health Stroke Scale scores.