The NIH Stroke Scale (NIHSS) is an 11-item neurological examination scale used to quantify neurological deficit in suspected acute stroke. It scores level of consciousness, gaze, visual fields, facial movement, limb strength, ataxia, sensation, language, dysarthria, and extinction or inattention.

The scale was described in the original 1989 Stroke paper as a structured bedside examination for acute cerebral infarction, with high inter-rater and test-retest reliability in early testing. It is now widely used to record baseline stroke severity, monitor early neurological change, and communicate severity across stroke teams.

Score	Common severity category
0	No stroke symptoms
1-4	Minor stroke
5-15	Moderate stroke
16-20	Moderate to severe stroke
21-42	Severe stroke

NIHSS reliability improves with standardised training and strict item definitions. The score can under-represent posterior circulation, gait, truncal ataxia, and some cognitive syndromes, so it should not be used alone to exclude reperfusion therapy, large-vessel imaging, or stroke-unit escalation.