A recent paper published in the American Journal of Epidemiology reports on a study by a Japanese scholar. The study followed 1071 Japanese people aged >40 years for 14 years (1998-2002). Of these, 42.7% smoked and 76.9% were H. pylori (Hp) infected. 68 cases of gastric cancer were detected during the 14-year period, with an interval from baseline to detection of gastric cancer ranging from 0.5 to 13.7 years. For patients with gastric cancer, the estimates for the population attribution analysis were 28.4% for smoking and 56.2% for Hp infection. Multifactorial analysis showed that the risk ratio for gastric cancer was 5.82 for smokers without Hp infection, 6.93 for nonsmokers with Hp infection, and up to 11.41 for smokers with both smoking and Hp infection compared with nonsmokers without Hp infection. The results of this study suggest that smoking and Hp infection have a synergistic effect on increasing the risk of gastric cancer.