O ne of the most common conditions causing respiratory difficulty in older patients is chronic obstructive pulmonary disease (COPD). It is a respiratory disorder largely caused by smoking, which is characterized by progressive, partially reversible airflow obstruction, systemic manifestations and exacerbations of respiratory distress that increase in frequency and severity over time. 1,2 Exacerbations of COPD, defined as the presence of an increase in at least 2 of breathlessness, sputum volume or sputum purulence, are a frequent cause of emergency department visits. 3 Chronic obstructive pulmonary disease is a major cause of morbidity and mortality in North America and Europe, and the rates of hospital admissions and visits to the emergency department have been rising over the past decade. 4 Many patients with COPD can be treated aggressively for exacerbation of COPD in the emergency department and improve sufficiently to be discharged safely within several hours. Discharging patients with adequate medications can prevent relapse or return to the emergency department because of worsening respiratory symptoms. 3 Many COPD exacerbations, however, are so severe that the patient must be admitted to hospital to ensure adequate management and a safe outcome. We previously showed a relatively low admission rate (38%) from ABSTRACT BACKGROUND: The Ottawa chronic obstructive pulmonary disease (COPD) Risk Scale (OCRS), which consists of 10 criteria, was previously derived to identify patients in the emergency department with COPD who were at high risk for short-term serious outcomes. We sought to validate, prospectively and explicitly, the OCRS when applied by phys icians in the emergency department.