OBJECTIVE: to determine how patterns of respiratory symptom change, patient behavior, and health status are related among patients with chronic obstructive pulmonary disease (COPD) and a history of exacerbations. METHODS: The study population was 421 community- dwelling adults with moderate to severe COPD. Symptom-based events (exacerbations) were defined to be any increase in at least one key symptom (dyspnea, sputum amount, sputum color) recorded in the daily diary on at least two consecutive days. An event was reported if it resulted in an exacerbation phone caU or documented health-care utilization. Predictors of reporting were assessed using a Cox proportional hazards model. RESULTS: Two-thirds of an events and 40% of events with 4 or more symptoms were not reported. Reporting an event was positively associated with a greater number of respiratory symptoms (HR:1.58, 95% CI: 1.37-1.81), a younger age (HR:1.12, 95% Cl:1.02-1.22 each 5 years), a lower FEV1 (HR:1.20, 95% CI:1.01-1.43 each 10% of predicted FEV1), and weekdays versus weekend (HR:3.03 and 95% CI:1.89-4.76). CONCLUSION: There was a high incidence of unreported exacerbations and sorne were important enough (4 or more symptoms) to have an indication for treatment. Reporting was related to the severity of exacerbation and underlying disease.