To determine if a delay in presentation to the emergency department (ED) after the onset of symptoms of an acute exacerbation of chronic obstructive pulmonary disease (AECOPD) increases the risk of hospital admission. A prospective cohort study utilizing data from 396 patient visits to 29 North American EDs. Inclusion criteria were age > or = 55 years; a diagnosis of COPD; and presentation for treatment of AECOPD, as defined by increasing shortness of breath, worsening cough, or change in sputum production at presentation. The median age was 69 years and 54% were female. Most patients (70%) presented to the ED > 24 hours after symptom onset, and most (61%) were hospitalized. On multivariate logistic regression analysis, after adjusting for 12 potential confounders (including demographics, clinical features, other diagnoses, and bronchodilator use before arrival), a delay in presentation > or = 24 hours was associated with a over two-fold increase in the odds of admission (odds ratio = 2.2, 95% confidence interval 1.1-4.8). This increase in risk persisted for delay in presentation > or = 12 hours in place of 24 hours, after restricting the analysis to patients admitted outside the intensive care unit, and to those reporting the ED as their usual site of care. A majority of patients delay presentation to the ED for > or = 24 hours after symptom onset, and are at higher risk of hospitalization. Early presentation should be emphasized to patients and caregivers to advance efforts to decrease the morbidity, mortality, and costs of AECOPD treatment.