Chronic obstructive pulmonary disease (COPD) exacerbations could represent an opportunity for pro-active COPD management rather than mere treatment if previously unknown disease is discovered; the extent of underdiagnosis and undertreatment of COPD in patients attending an emergency department (ED) with an exacerbation is not known. During 2002, we recalled 131 COPD patients in stable conditions, 4-8 weeks after they had attended the ED or been discharged from our University Hospital (North-West of Italy). Information on diagnosis and management prior to the ED attendance were collected; spirometry and arterial blood gas analyses were performed. One-third of patients had never been diagnosed and treated even though 83% of them had moderate-to-very-severe COPD and about 30% already had respiratory failure. Only 20% had received information on the nature of the disease and none had received a written action plan. Only 60% were receiving long-acting bronchodilators and 41% of patients with respiratory failure were receiving long-term oxygen. A substantial number of undiagnosed and untreated patients with moderate-to-very-severe COPD came to our attention through an exacerbation. This enforces the importance of exacerbations as the starting point of pro-active COPD management and of the ED as a valuable sentinel to identify this subset of patients.