Introduction The purpose of the study was to assess the functional abilities of patients after stroke and to identify factors that affect it. Material and methods The study was performed on 40 patients after stroke. To assess functional ability the Rivermead Motor Assessment (RMA), Barthel Index (BI), Tinetti test, and Up&Go test were used. The maximum muscle power (Pmax), optimal shortening velocity (Vopt), muscle strength, one-leg standing test, Geriatric Depression Scale (GDS), pain assessment (Numeric Pain Scale), nutrition assessment (Mini Nutritional Assessment Scale - MNA) were also performed. Results Functional performance was influenced by: knee flexors on the affected side (correlations respectively: RMA rho=0,37; p=0,04; Tinetti test rho=0,44; p<0,01; Up&Go test rho=-0,56; p<0,001), balance time on a non-affected leg (RMA rho=0,38; p=0,03; BI rho=0,41; p=0,01; test Tinetti rho=0,64; p<0.001; Up&Go test rho=-0.47; p=0.003), Pmax (RMA rho=0,35; p=0,04; Tinetti test rho=0,49; p<0,01; Up&Go test rho=-0,63; p<0.001), reporting problems with sitting and standing up (RMA p=0,003; Tinetti test p=0,02; Up&Go test p=0.049), using orthopedic assistance (RMA global functions p=0,01; RMA lower limb and torso p=0,04; BI p=0,003; Tinetti test p<0,001, Up&Go test p<0,001). The MNA result was correlated with RMA (rho=0,36; p ,0.04), no correlation was obtained for any of the functional tests with the extensor muscle strength on the non-affected side, GDS and pain level. Conclusions The functional ability of stroke patients is affected by knee flexors on the affected side, the ability to maintain balance, and maximum muscle power. People, who reported problems with sitting and standing up and using orthopedic assistance, are characterized by worse ability.