Objective: Clopidogrel is commonly co-prescribed with aspirin in patients with heart disease, and therefore the associated risk of gastrointestinal adverse events may be high. We sought to determine the incidence of medical claims for potential gastrointestinal adverse events among clopidogrel users in an administrative database. Methods: Clopidogrel users were identified in a large US database (representing a network of over 70 managed care plans) based on the following criteria: an initial clopidogrel prescription between between October 2003 and January 2004, a clopidogrel-free window in the prior 6 months, and at least 24 months of continuous eligibility over the study time-frame. ICD9 codes were used to identify new peptic ulcer and gastrointestinal bleeding events in the 12 months after the first clopidogrel prescription. Results: There were 368,061 subjects identified who met the selection criteria. Of these subjects, 58% were male and 72% were greater than or equal to 60 years of age. The average duration of clopidogrel use was 200 days. The proportion having a medical claim for peptic ulcer or gastrointestinal bleeding was 6.2%. Higher incidences were seen in women compared to men (7.4% vs. 5.4%; p<0.000001) and those who were greater than or equal to 60 years of age compared to those under 60 (6.9% vs. 4.3%; p<0.000001). Conclusion: There is a high incidence of medical claims for peptic ulcer or upper gastrointestinal bleeding among patients who receive clopidogrel, especially in women and those who are greater than or equal to 60 years of age.