Obesity and arthritis are critical public health problems with high prevalences and medical costs. In the United States, an estimated 72.5 million adults aged ≥20 years are obese, and 50 million adults have arthritis. Medical costs are estimated at $147 billion for obesity and $128 billion for arthritis each year.1-3 Obesity is common among persons with arthritis2 and is a modifiable risk factor associated with progression of arthritis, activity limitation, disability, reduced quality-of-life, total joint replacement, and poor clinical outcomes after joint replacement.4,5 To assess obesity prevalence among adults with doctor-diagnosed arthritis, CDC analyzed data from the Behavioral Risk Factor Surveillance System (BRFSS) for the period 2003-2009. This report summarizes the results of that analysis, which determined that, among adults with arthritis, (1) obesity prevalence, on average, was 54% higher, compared with adults without arthritis, (2) obesity prevalence varied widely by state (2009 range: 26.9% in Colorado to 43.5% in Louisiana), (3) obesity prevalence increased significantly from 2003 to 2009 in 14 states and Puerto Rico and decreased in the District of Columbia (DC), and (4) the number of U.S. states with age-adjusted obesity prevalence ≥30.0% increased from 38 (including DC) in 2003 to 48 in 2009. Through efforts to prevent, screen, and treat obesity in adults, clinicians and public health practitioners can collaborate to reduce the impact of obesity on U.S. adults with arthritis.