Introduction: Clopidogrel is widely used in developed and developing countries for preventing and treating atherothrombotic complications due to atherosclerosis. However, some patients show clopidogrel resistance in vitro with insufficient inhibition of platelet function. This study aimed to estimate the frequency of clopidogrel resistance in elderly patients based on the platelet closure time and to identify risk factors. Material and Methods: This cross-sectional study was carried out between December 2017 and May 2018 at the University Hospital of Sidi Bel Abbes. Platelet closure time was measured using the P2Y cartridge with the Platelet Function Analyzer (PFA). Clopidogrel non-response was defined as a P2Y platelet closure time less than 106 seconds. Results: We enrolled 73 patients aged 65 year old and over in the study. Two patients were excluded because of a hematocrit less than 25%. A total of 71 subjects was included in our analysis. The sex ratio male/female was 1.15. The frequency of clopidogrel resistance in elderly patients was 18.3%, with a 95% confidence interval CI (9.30-27.3). Among the factors examined (age, sex, body mass index, tobacco, diabetes, arterial hypertension, chronic kidney failure, dyslipidemia, personal history of myocardial infarction, clopidogrel dose, associated drugs, hyperleukocytosis), only arterial hypertension was significantly associated with in vitro clopidogrel resistance p = 0.035, OR =4.525 95% CI (1.114-18.38). Conclusion: A significant rate of elderly patients did not respond to clopidogrel, which put them at a higher risk of developing thrombo-ischemic events. Point-of-care testing can help to identify these patients who may then benefit from alternative antiplatelet therapy.