Pathogenesis of osteoarthritis may have a systemic metabolic component. This study was undertaken to assess the prevalence of primary knee osteoarthritis (OA) in a sample of Egyptian patients with metabolic syndrome (MetS) and to examine the relationship of metabolic syndrome and its components with clinical, functional, and radiographic findings of knee OA. A total of 60 patients (55 females, 5 males) diagnosed as having MetS according to the National Cholesterol Education Program Adult Treatment Panel III (ATP III) criteria and 30 obese subjects without MetS (24 females, 6 males), serving as a control group, were included in this study. All participants had completed preliminary questionnaires, clinical and laboratory examinations, and an evaluation for radiographic knee OA. Scores from the Western Ontario and Mc-Master University (WOMAC) were used for the pain, stiffness, and disability assessments of OA patients. X-rays were classified according to the Kellgren-Lawrence (KL) radiographic rating scale. We tested the relationship of metabolic syndrome and its components with the WOMAC score and radiographic findings of knee OA after adjusting for BMI. The prevalence of OA was 83.3% in MetS group compared with 63.3% in control group (P = 0.034). MetS patients with OA had higher WOMAC score and radiographic grading than controls with OA (P = 0.034, 0.019). MetS patients with OA had more waist circumference (WC) (P = 0.022), and higher frequency of hypertension (HTN) and diabetes mellitus (DM) (P = 0.009, 0.002 respectively) than MetS patients without OA. There were significant associations of MetS, WC, HTN, DM, high TG, and low HDL with OA (P = 0.041, 0.007, < 0.001, < 0.001, 0.016, 0.012 respectively) by linear regression analysis. There were also significant associations of MetS with WOMAC score and X-ray grading (P = 0.003, 0.019 respectively) by linear regression analysis. Knee OA is prevalent in patients with MetS and associated with worse pain and functional impairment score and advanced radiographic changes. Abdominal obesity, hypertension, and diabetes are the most common components of MetS in patients with knee OA.