Background The risk of clinical deterioration still exists in the acute phase despite the fact that patients with minor stroke may display less severe symptoms.The impact of this clinical deterioration on long-term outcomes is unknown.We characterized the clinical features of neurological deterioration (ND) in the acute phase of minor ischemic stroke (MIS) and investigated its impact on mid-and long-term outcomes.Methods This was a multi-centered,prospective clinical study involving patients with MIS (the National Institutes of Health Stroke Scale,NIHSS ＜3) recruited from the China National Stroke Registry.Patients were included who had been hospitalized within 24 hours of stroke onset.Baseline characteristics,complication rates during hospitalization,etiology of stroke,as well as 3-,6-,and 12-month post-stroke outcomes were compared between patients with and without ND during the acute phase.Results A number of 368 (15.2％) out of 2424 patients included in the study exhibited ND in the acute phase.Compared to patients without ND,patients with ND had longer hospital stay,increased rate of baseline diabetes,and multiple complications.Multivariate Logistic regression indicated that ND in acute phase was an independent factor predictive of increased dependence (adjusted odds ratio =5.20,95％ Cl,3.51-7.70,P ＜0.001) at 12-month post-stroke.Conclusions The risk of ND in the acute phase is high in patients with MIS.ND in the acute phase is an independent predictor for poor outcomes at 12 months post-stroke onset.