Objective. To determine whether thigh muscle strength differs between symptomatic and asymptomatic knees, and/or different radiographic strata of knee osteoarthritis (KOA). Results. Isometric strength was significantly lower in symptomatic than in asymptomatic legs: ؊11 to ؊13% for extensor strength and ؊7 to ؊16% for flexor strength (P < 0.0001 for both) in men, and ؊9 to ؊17% (P ؍ 0.029) for extensor strength, and ؊10 to ؊21% (P ؍ 0.049) for flexor strength in women. Similar observations were made for pain frequency strata. Extensor and flexor strength were not significantly different across K/L grade strata in asymptomatic legs in either sex (P > 0.12). However, strength normalized to body weight was lower at higher K/L grades in both sexes (P < 0.02) because the body mass index was greater in participants with more advanced radiographic disease. Conclusion. Knee symptoms (i.e., pain) appear to be the relevant determinant of isometric knee extensor and flexor strength in KOA, whereas no direct association between strength and radiographic severity was observed. These findings suggest that the reduction in thigh muscle strength in KOA is related to pain but not to the structural (radiographic) disease status.