Objective: This study investigated the effect of hypermobility on pain, joint stiffness, physical function, and quality of life in patients with knee osteoarthritis. Design: Sixty-four patients diagnosed with bilateral knee osteoarthritis were included; 42 patients in Group 1 were those with hypermobility and 22 patients in Group 2. There were 40 women and 2 men in Group 1, and 16 women and six men in Group 2 were those without hypermobility. The age, sex, and body mass index of all patients recorded. The WOMAC and SF-36 tests performed on the patients.Results: The average ages were 51.40±5.42 and 53.36±4.31, respectively, and there was no statistically significant difference. The body mass index was high in the hypermobility group, and the difference was statistically significant (p=0.028). Pain and stiffness were higher in the hypermobility group than in the non-hypermobility group in the WOMAC subgroups and total scores (p=0.030, p=0.002, p=0.047). The non-hypermobility group had better SF-36 social function and pain scale scores. The difference was statistically significant (p=0.016, p=0.004).Conclusions: Hypermobility aggravates the symptoms of knee osteoarthritis. Hypermobility evaluated in all patients diagnosed with knee OA. A more intense and long-term rehabilitation program should be determined for these patients to prevent injuries and improve proprioception.