The majority of adults > 55 years of age show radiographic evidence of osteoarthritis; however, determining definitive prevalence and incidence rates of knee osteoarthritis and hip osteoarthritis poses methodologic problems. Several factors play a role in osteoarthritis risk, including age, gender, genetics, behavioral influences, and ethnicity. Studies cited compare data from the Framingham Osteoarthritis Study with data from studies performed in Asian and European populations. A number of broad trends stand out, including higher prevalence in advanced age for both hip and knee osteoarthritis, with higher prevalence and incidence in women than in men.