Introduction/Objective. Pain, stiffness and limited mobility are the main factors that lead to difficulties in performing daily activities and are also responsible for the decline in the quality of life in people with knee osteoarthritis (OA). The aim of this study was to evaluate the functional capacity and health related quality of life (HRQoL) compared to pain in patients with knee OA, as well as to determine the correlation between these three clinical variables. Methods. The study involved 931 patients diagnosed with knee OA. In all patients, pain was evaluated by a short form of the McGill pain questionnaire (SF-MPQ), functional status was assessed using the Western Ontario and McMaster Universities Arthritis Index (WOMAC), while life quality was evaluated using the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Results. The average age of patients was 61.21 ? 4.62 years, while 71.3% of them were women. The quality of life in patients with knee OA and all pain parameters contained in the SF-MPQ were highly statistically positively associated (p ? 0.01). In addition, the physical functioning was mostly affected by emotional pain (rho = -0.585). A high statistical correlation (p ? 0.01) was noted between stiffness and physical functioning from the WOMAC questionnaire and all of the parameters from the SF-MPQ. The physical functioning from the WOMAC questionnaire had the strongest correlation with total pain incorporated into the McGill questionnaire (rho = 0.530). Conclusion. Knee pain has a significant impact on functional capacity and HRQoL in patients with knee OA. Therefore, one of the main therapy goals for OA of the knee should be to reduce the pain in the affected knee, which can help to improve the functionality and HRQoL of these patients.