BACKGROUND AND OBJECTIVE: We tested the hypothesis that gastro-esophageal reflux disease is a risk factor for exacerbations in individuals with chronic obstructive pulmonary disease (COPD). METHODS: Among 9622 participants in the Copenhagen City Heart Study, we identified 1259 individuals with COPD and information on gastro-esophageal reflux disease and the regular use of acid inhibitory treatment. These individuals were followed for 5 years with regard to medically treated COPD exacerbations, which we defined as a short course treatment with oral corticosteroids alone or in combination with antibiotics. We applied a multivariable Cox regression analysis with adjustment for well-established risk factors associated with COPD exacerbations or gastro-esophageal reflux disease, including COPD severity, and symptoms. RESULTS: Individuals with COPD and gastro-esophageal reflux disease had more chronic bronchitis (31 vs 21%, P = 0.004), more breathlessness (39 vs 22%, P < 0.001), and more of them had a history of respiratory infections (6.8 vs 1.4%, P < 0.001) than individuals with COPD but without gastro-esophageal reflux disease. Among individuals with COPD and gastro-esophageal reflux disease, those who did not use acid inhibitory treatment regularly had an increased risk of COPD exacerbations during follow-up, hazards ratio (HR): HR = 2.7 (1.3-5.4, P = 0.006). Individuals with gastro-esophageal reflux disease, using acid inhibitory treatment regularly did not have an increased risk of exacerbations, HR = 1.2 (0.6-2.7, P = 0.63). CONCLUSIONS: Gastro-esophageal reflux disease was associated with an increased risk of medically treated exacerbations of COPD, but only in those individuals who did not use acid inhibitory treatment regularly.