In this study, we aimed to disclose the net effect of long-term (6-month) clopidogrel treatment as compared to that of short-term (1-month) treatment in the poststenting period. A total of 278 patients with successful stent implantation were involved in the study. After preloading with 300 mg of clopidogrel orally (p.o.) 24 h prior to the procedure, randomly selected patients were given either 75 mg p.o. for 1 month (group A) or 75 mg p.o. for 6 months (group B). The patients were followed up clinically and underwent control angiography at 6 months regardless of their clinical status to delineate the coronary anatomy and assess quantitative computer-assisted (QCA) analysis. In 140 (50.4%) patients (group A), 244 (50.6%) stents were used to treat 237 coronary lesions, and in 138 patients (group B), 238 (49.4%) stents were used to treat 238 coronary lesions. There was no difference between the groups with respect to any of the clinical characteristics, intracoronary thrombus, antiaggregant therapy, the type of lesion, vessel score index, and baseline QCA parameters. In 62 patients binary in-stent restenosis (ISR) was determined with no statistical difference between the groups (group A: 20.7% vs group B: 23.9%, P = not significance). There was also no difference between the two groups at 6 months regarding QCA parameters. Thirty-seven of the 62 patients with restenosis have developed major adverse coronary events such as death, myocardial infarction, and target vessel revascularization (group A: 12.9% vs group B: 13.8%, P = not significant). In patients with chronic coronary syndrome, in the poststenting period, 6-month clopidogrel use as an adjunct to aspirin has shown no benefit over 1 month use with respect to clinical outcome and angiographic outcome, such as restenosis rate, follow-up, minimal luminal diameter, late loss, lost index, and net gain.