Background In-hospital medical complications are associated with poorer clinical outcomes for stroke patients after disease onset.However,few studies from China have reported the effect of these complications on the mortality of patients with acute ischemic stroke.In this prospective work,the China National Stroke Registry Study,we investigated the effect of medical complications on the case fatality of patients with acute ischemic stroke.Methods From September 2007 to August 2008,we prospectively obtained the data of patients with acute stroke from 132 clinical centers in China.Medical complications,case fatality and other information recorded at baseline,during hospitalisation,and at 3,6,and 12 months after stroke onset.Multivariable Logistic regression was performed to analyze the effect of medical complications on the case fatality of patients with acute ischemic stroke.Results There were 39741 patients screened,14526 patients with acute ischemic stroke recruited,and 11560 ischemic stroke patients without missing data identified during the 12-month follow-up.Of the 11560 ischemic patients,15.8％ (1826)had in-hospital medical complications.The most common complication was pneumonia (1373;11.9％ of patients),followed by urinary tract infection and gastrointestinal bleeding.In comparison with patients without complications,stroke patients with complications had a significantly higher risk of death during their hospitalization,and at 3,6 and 12 months post-stroke.Having any one in-hospital medical complication was an independent risk factor for death in patients with acute ischemic stroke during hospital period (adjusted OR=6.946;95％ CI 5.181 to 9.314),at 3 months (adjusted OR=3.843;95％ Cl 3.221 to 4.584),6 months (adjusted OR=3.492;95％ CI 2.970 to 4.106),and 12 months (adjusted OR=3.511;95％ Cl 3.021 to 4.080).Having multiple complications strongly increased the death risk of patients.Conclusion Short-term and long-term outcomes of acute stroke patients are affected by in-hospital medical complications.