The NIH Stroke Scale is a 15-item neurological examination scale used to evaluate the effect of acute stroke on consciousness, language, neglect, visual fields, eye movement, motor strength, ataxia, dysarthria, and sensory loss. Scores range from 0 to 42.

NIHSS 0: no stroke symptoms. 1–4: minor stroke — may not require thrombolysis. 5–15: moderate stroke — generally eligible for IV tPA within 4.5 hours. 16–20: moderate-severe — consider IV tPA and thrombectomy. 21–42: severe stroke — consider thrombectomy.

IV tPA (alteplase) is typically considered for NIHSS ≥4 within 4.5 hours of symptom onset. Mechanical thrombectomy may be beneficial for large vessel occlusions with NIHSS ≥6 up to 24 hours in selected patients. Lower scores may still warrant treatment based on disabling symptoms.

The NIHSS has good inter-rater reliability when administered by trained personnel. Formal certification is required for clinical trial use and is recommended for clinical practice. The scale takes approximately 5–8 minutes to administer.