Infection with Helicobacter pylori (Hp) is considered a prerequisite for gastric carcinogenesis and gastric mucosal atrophy that develops in association with the infection is a risk factor for gastric cancer. The gastric cancer risk can be diagnosed by the ABC classification consisted of a combination of serum Hp antibody and the pepsinogen (PG) method. The ABC classification may contribute to gastric cancer screening as well as to primary care of digestive organ practice. However, we should remember that we cannot diagnose the gastric cancer by only the ABC classification, and an imaging examination is required.