OBJECTIVES: Obesity has been associated with disease outcomes in inflammatory arthritis. This study aimed to investigate cross-sectionally the relationship between body mass index (BMI) and functional disability in a large inception cohort of patients with early inflammatory polyarthritis (IP) METHODS: Patients age ≥16 with ≥2 swollen joints for ≥4 weeks were recruited into the Norfolk Arthritis Register (NOAR). At initial assessment, clinical and demographic data were obtained; joints examined, and height and weight measured. Blood samples were taken to measure inflammatory markers and autoantibodies, and patients completed the Health Assessment Questionnaire (HAQ) to assess functional disability. Univariate and multivariate ordinal regression were used to examine the cross-sectional association between BMI and HAQ. Multiple imputation using chained equations allowed inclusion of patients with missing variables. RESULTS: 1246 patients were studied, median age 57 years. 782 (63%) patients were female, 303 (25%) were obese (BMI ≥30 kg/m(2) ). Morbid obesity (BMI ≥35) was significantly associated with worse functional disability in the univariate and multivariate analysis with missing data imputed, adjusting for age, gender, symptom duration, smoking status, disease activity, autoantibodies, comorbidities and treatment(multivariate OR=1.87, 95% CI 1.14-3.07). CONCLUSIONS: Morbid obesity in patients with early IP is associated with worse HAQ scores. This should be taken into account in patient management and when interpreting HAQ in clinical practice. © 2012 by the American College of Rheumatology.