PURPOSE: This study was conducted to investigate the epidemiologic characteristics of knee osteoarthritis (OA) in elderly Koreans with respect to its detailed prevalence and association with demographic factors such as gender, age and body mass index (BMI). MATERIALS AND METHODS: Six hundred and ninety six subjects (men 298 and women 398) aged 65 years or older were recruited from an urban population. Radiographic evaluations were conducted using three plain radiographs (weight bearing anteroposterior view, 45 degree of flexion posteroanterior view, and the Merchant view). Radiographic severity was determined using the Kellgren-Lawrence (K/L) grading scale and radiographic OA was defined as K/L grade 2 or higher. Overall prevalence of OA was analyzed with regard to gender, age and BMI using multivariate logistic regression. RESULTS: The overall prevalence of knee OA in the study cohort was 38.1%. Women had the much higher prevalence of knee OA than men (53.8% vs. 17.1%). Female gender, obesity and ageing were associated with the risk of knee OA, but a female gender was found to be the strongest predictor for knee OA. CONCLUSION: This study documents that knee OA is highly prevalent among Korean elderly, and that elderly Korean women are at much greater risk of development of knee OA. It is hoped that our findings provide information that aids the creation of national health policies that better target the prevention and treatment of knee OA.