OBJECTIVES To quantify the relative risk of epistaxis for patients taking low-dose aspirin or clopidogrel compared to patients taking neither drug. DESIGN Case-control study. SETTING Primary care. PARTICIPANTS 10,241 patients from three GP practices in the West Midlands. MAIN OUTCOME MEASURES Epistaxis resulting in presentation to the GP, attendance at Accident & Emergency, or referral to ENT outpatients. RESULTS There was a significant difference in the proportion of patients with epistaxis across the three groups (chi(2) = 84.1; 2 degrees of freedom; P < 0.000001). Relative risk of epistaxis was increased in both the aspirin (RR = 9.04; 95% CI = 5.13-15.96) and clopidogrel (RR = 6.40; 95% CI = 2.33-17.56) groups compared to the no drug group. There was no increased risk of epistaxis with aspirin compared to clopidogrel (RR = 1.4; 95% CI = 0.6-3.4). CONCLUSION There is an increased risk of troublesome epistaxis in patients taking aspirin or clopidogrel. There is no significant difference in risk of epistaxis between the two drug groups.