BACKGROUND: Obesity contributes to respiratory symptoms and exercise limitation, but the relationships between obesity, airflow obstruction (AO), respiratory symptoms and functional limitation are complex. AIMS: To determine the relationship of obesity with airflow obstruction (AO) and respiratory symptoms in adults without a previous diagnosis of chronic obstructive pulmonary disease (COPD). METHODS: We analysed data for potential referents recruited to be healthy controls for an ongoing study of COPD. The potential referents had no prior diagnosis of COPD or healthcare utilisation attributed to COPD in the 12 months prior to recruitment. Subjects completed a structured interview and a clinical assessment including body mass index, spirometry, six-minute walk test (SMWT), and the Short Performance Physical Battery (SPPB). Multiple regression analyses were used to test the associations of obesity (body mass index >30kg/m2) and smoking with AO (forced expiratory volume in 1s/forced vital capacity ratio <0.7). We also tested the association of obesity with respiratory symptoms and impaired functional capacity (SPPB, SMWT), adjusting for AO. RESULTS: Of 371 subjects (aged 40-65 years), 69 (19%) had AO. In multivariate analysis, smoking was positively associated with AO (per 10 pack-years, OR 1.24; 95% CI 1.04 to 1.49) while obesity was negatively associated with AO (OR 0.54; 95% CI 0.30 to 0.98). Obesity was associated with increased odds of reporting dyspnoea on exertion (OR 3.6; 95% CI 2.0 to 6.4), productive cough (OR 2.5; 95% CI 1.1 to 6.0), and with decrements in SMWT distance (67+/-9m; 95% CI 50 to 84m) and SPPB score (OR 1.9; 95% CI 1.1 to 3.5). None of these outcomes was associated with AO. CONCLUSIONS: Although AO and obesity are both common among adults without an established COPD diagnosis, obesity (but not AO) is linked to a higher risk of reporting dyspnoea on exertion, productive cough, and poorer functional capacity.