BACKGROUND: Helicobacter pylori(H. pylori) is a major risk factor for chronic gastritis, peptic ulcer, and low grade gastric lymphoma of mucosa-associated lymphoid tissue(MALT). Eradication of H. pylori can induce prevention of peptic ulcer relapse and regression of gastric MALT lymphoma. Smoking has also been knawn to be a mapr risk factor for peptic ulcer. The purpose of this study is to evaluate the effects of smoking on eradication of H. pylori according to smoking status, amount of smoking, and smoking cessation. METHODS: We studied 132 patients with H. pylori-positive gastroduodenal diseases. Diseases composed of gastritis in 36.4%, peptic ulcer 62.1%, gastric MALT lymphoma 1.5%. Patients were treated with amoxacillin 1.0g, clarithromycin 500mg, omeprazole 20mg bid for a period of 7 days. Patients underwent a follow-up gastroendoscopy 6 weeks later after eradication treatment. H. pylori status was confirmed by initial and follow up biopsies of gastric antrum and corpus using Hematoxylin-Eosin stain and Wharthin-Starry silver stain. At the begining of treatment, 66.7% of 132 patients were smokers, 9.8% ex-smokers, 23.5% non-smokers. Smokers were advised to stop smoking through education and counseling at each office visit. RESULTS: H. pylori eradication was achieved in 111 patients(84.1%). The number of smokers who had quit smoking sucessfully during treatment were 25(28.4%). The rate of eradication did not seem to influenced by initial smoking status and total amount of smoking(pack-years). Hawever, during treatment, success group for smoking cessation(100%) had a higher rate of eradication than non-cessation group. Daily amount of smoking had an effect on eradication with significant statistical difference ; Non-smokers showed 89.9% eradication rate, mild smokers(<20 cigarettes/day) 81.8%, and heavy smokers ( >20/day) 50%. CONCLUSIONS: These results suggest that current smoking status and daily amount of smoking during treatment seem to influence the rate of eradication of H. pylori rather than past smoking history alone. There was some improvement in the eradication rate by quitting or reducing smoking together with H. pylori eradication treatment.