Objective To detect the association between subclinical hyperthyroidism and early neurological deterioration (END) in patients with acute cerebral infarction.Methods Totally 139 patients diagnosed with acute ischemic stroke were prospectively enrolled between March 2015 and September 2016.The early neurological deterioration was defined as 7-day in-hospital increase (vs.that at admission) in the NIHSS score of ≥2 points without any systemic cause.Multivariable Logistic regression analysis was conducted to evaluate the relationship between subclinical hyperthyroidism and END.Subclinical hyperthyroidism is defined as TSH ＜ 0.44 mU/L,with normal FT3 and FT4.Multivariable Logistic regression analysis was conducted to evaluate the relationship between subclinical hyperthyroidism and END.Results 42 (30.2％) patients with END among 139 with subclinical hyperthyroidism were observed.As compared with patients without END,patients with END showed older age[(71.2±5.7) years vs.(68.1±6.3) years,t=2.695,P=0.008],higher prevalence of subclinical hyperthyroidism (28.6％ vs.9.3％,x2 =8.506,P=0.006),and higher levels of C-reactive protein[5.6 (1.0,11.0) mg/L vs.2.5 (1.0,5.0) mg/L,Z=2.125,P=0.034],homocysteine[(15.3±5.8) mmol/L vs.(13.0±4.8) mmol/L,t=2.395,P=0.018]and fasting bloodglucose[(8.1 ± 2.2) mmol/L vs.(6.3 ± 2.6) mmol/L,t =4.108,P =0.001].Logistic regression analysis indicated that subclinical hyperthyroidism was associated with END after adjustment for potential confounders (OR =3.415,95 ％ CI:1.148-10.167,P =0.027).Conclusions Subclinical hyperthyroidism is a significant and independent predictor for END in patients with acute cerebral infarction.