•The trunk muscle mass of stroke patients is related to the discharge Functional Independence Measure-motor score.•This association is stronger than that between the Functional Independence Measure-motor score and the appendicular skeletal muscle mass index.•Self-care and locomotion are associated with trunk muscle mass in stroke patients.•Transfer and locomotion are associated with appendicular skeletal muscle mass. The aim of this study was to evaluate the effects of trunk muscle mass on functional prognosis, including activities of daily living (ADLs), at hospital discharge in patients with acute stroke. This retrospective cohort study included hospitalized patients with acute stroke. Trunk muscle mass was measured using bioelectrical impedance analysis within 5 d of admission. The primary outcome was ADLs at hospital discharge, assessed using the Functional Independence Measure-motor items (FIM-motor). The secondary outcomes were hospital length of stay and discharge to home. Multivariate analyses were performed to determine the association between trunk muscle mass and FIM subitems. Data from 212 patients (mean age 72.7 y; 143 men) were included in the analysis. The median trunk muscle mass index (TMI) was 8.2 kg/m2 in men and 6.7 kg/m2 in women. Patients in the high TMI group were younger and had a higher FIM-motor score at discharge (P < 0.001). In multivariate analyses, TMI was positively associated with the FIM-motor score at discharge (β = 0.240, P < 0.001). FIM-self-care (β = 0.351, P < 0.001) and locomotion (β = 0.331, P < 0.001) were positively associated with the TMI. Trunk muscle mass is associated with ADLs at hospital discharge after acute stroke. TMI is important for evaluating functional prognosis in patients with acute stroke.