- To examine the associations of sex, body mass index (BMI), and age with knee osteoarthritis (OA) symptomatic severity. A cross-sectional retrospective analysis. Patients completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire and Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Data were acquired from a stored database of a private therapy center. Patients (N=1487) with symptomatic knee OA were evaluated. Not applicable. WOMAC questionnaire and SF-36. BMI correlated significantly with worse knee OA symptoms for all WOMAC and SF-36 subcategories (all P ≤.001). Age correlated significantly with worse symptoms only for WOMAC function and SF-36 physical functioning (P=.001 and P=.009, respectively). A significant difference across BMI quintiles was found for all WOMAC and SF-36 subcategories (all P ≤.01). Women showed worse knee OA symptoms in all WOMAC and SF-36 subcategories (all P ≤.001). There was a significant interaction of sex by BMI in WOMAC pain and WOMAC function (P=.01 and P=.02, respectively). Based on the results of this analysis, it can be concluded that women and patients with a higher BMI with knee OA are at a greater risk for worse symptoms.