To evaluate the convergent validity and responsiveness of the Stroke Upper Limb Capacity Scale (SULCS) in comparison to the Arm Motor Ability Test (AMAT), the Box and Blocks Test (BBT), and the upper limb Fugl-Meyer Assessment (FMA). The SULCS is a relatively new measure that was designed to be easier to score and less time consuming than some existing measures.Prospective repeated-measures design.Clinical research laboratory of a large public hospital.Patients (N=61) <2 years poststroke with moderate to severe upper limb hemiparesis.Participants received 12 weeks of therapy that included neuromuscular electrical stimulation of the paretic finger and thumb extensors. The SULCS, AMAT, BBT, and FMA were administered at weeks 0, 6, 12 (end of therapy), 20, 28, and 36 (6mo post-therapy).Convergent validity was evaluated with Spearman's correlation coefficients between pairs of measures at each time point. Responsiveness from 0 to 12 weeks and 0 to 36 weeks was evaluated with the standardized response mean (SRM).The SULCS demonstrated strong correlation with the AMAT (ρ=0.81-0.93), BBT (ρ=0.73-0.92), and FMA (ρ=0.78-0.92), at all 6 time points. All 4 measures had moderate to large SRMs (SULCS, 0.71-0.77; AMAT, 0.83-0.97; BBT, 0.73-0.82; FMA, 0.75-0.76). There was no significant difference in responsiveness among the 4 measures.The results support the use of the SULCS to measure upper limb capacity in patients who are less than 2 years poststroke with moderate to severe hemiplegia.