The aim of this study was to determine the validity of the Stroke Upper Limb Capacity Scale (SULCS) and its three hand categories in an acute inpatient stroke rehabilitation setting. We included 312 persons, about 10 days poststroke, with a mean National Institutes of Health Stroke Score (NIHSS) of 7.3. Participants were also assessed on the functional independence measure (FIM), Upper Extremity–Motricity Index (UE-MI), modified Charlson Comorbidity Index, and proportion of home discharges. Spearmans rho between total SULCS and FIM-self-care score and UE-MI at admission were strong at 0.72 and 0.82, respectively. Correlations were stronger between SULCS and individual FIM items of eating, grooming, and bathing [rho= 0.52–0.57, that is, ‘more’ activity of daily living (ADL)-like items] rather than walking, bowel, and expression (rho= 0.28–0.51, that is, ‘less’ ADL-like items). Admission and discharge FIM, NIHSS, and proportion of home discharges were higher with more favorable SULCS hand categories. Floor effect was 11.9% and ceiling effect was 14.7% with an acceptable internal consistency (Cronbach’s alpha of 0.92). The SULCS is a valid measure of upper extremity capacity at admission to inpatient stroke rehabilitation. Further examination regarding ceiling effects and responsiveness in inpatient stroke rehabilitation is recommended.