Persistent cough could be caused by various diseases such as postnasal drip syndrome, asthma and gastroesophageal reflux disease (GERD) or adverse event of drugs such as angiotensin-converting enzyme inhibitors. We report a case of persistent cough associated with high plasma levels of the proton pump inhibitor omeprazole in a patient with GERD. This case suggests cough as an adverse drug event to omeprazole, which is otherwise commonly prescribed for the management of GERD-related cough. Therefore, physicians should be aware of the onset or an exacerbation of cough during omeprazole therapy.