The factors associated with an increase in gastric cardia adenocarcinoma are poorly understood. Environmental factors such as Helicobacter pylori ( H. pylori) infection and diet have been hypothesized to play a role in the recently increased risk of this disease, but additional studies are needed. In conducting studies to establish the relationship between potential risk factors and gastric cardia adenocarcinoma, it is necessary to carefully consider the role of bias. In a recently published study, the reported associations between H. pylori as well as post-meal physical exertion and gastric cardia adenocarcinoma may have been greatly influenced by selection bias.