The Confronting Chronic Obstructive Pulmonary Disease (COPD) Survey in North America and Europe conducted during 1999-2000 aimed to identify international differences in the clinical management of COPD and the patients' perspectives on their disease. Our aim was to validate the screening questionnaire used in this study in a sample of patients presenting at a respiratory clinic. Interviews were conducted at an outpatient clinic of the London Chest Hospital. Of the 136 patients contacted, 25 refused or were not able to participate. Questionnaire data were validated by comparison with medical records and spirometry on 104 patients. Overall, the questionnaire correctly identified 86.5% of patients with a diagnosis of COPD with a chance-corrected agreement (kappa = 0.66, SE 0.098), which indicates good agreement between the questionnaire alpha and the medical records. The questionnaire had a high sensitivity (92.0%) and specificity (72.4%) with respect to the diagnosis of COPD. The screening questionnaire used in The Confronting COPD Survey appears to be a valid screening tool to differentiate COPD from other respiratory diseases.