OBJECTIVE: The aim of this study was to determine if the arm-subscore of the Motricity Index (AMI) 1 week following stroke can predict recovery of upper extremity function according to the Action Research Arm Test (ARAT) prior to inpatient rehabilitation facility (IRF) discharge and at 3-months outpatient follow-up. DESIGN: This was a prospective cohort study of patients with acute ischemic stroke admitted to a single acute care hospital and affiliated IRF between 2016 and 2018. Upper extremity dexterity of the impaired limb was assessed using the AMI and ARAT. Receiver operating characteristic (ROC) curve analysis was used to determine optimal cut-offs of the initial AMI for a good functional outcome defined as ARAT≥45. RESULTS: Ninety-five patients were evaluated at median 6, 26, and 98.5 days following stroke. Median [interquartile range (IQR)] AMI at 1-week was 77 [20.3-93]. Median [IQR] ARAT scores prior to IRF discharge and at 3-months outpatient follow-up were 33 [3.5-52] and 52 [34-55.8], respectively. The optimal AMI to predict ARAT≥45 prior to IRF discharge and at 3-months outpatient follow-up were 71 and 58, respectively. CONCLUSION: Early AMI at 1-week predicts upper extremity functional capacity prior to IRF discharge and at 3-months outpatient follow-up.