The current study was conducted to determine the prevalence of Helicobacter pylori in the oral cavity of a Chinese population. Nested polymerase chain reaction (PCR) was used to investigate whether individuals with oral H. pylori show more possibility of gastric infection and to examine the relationship between gastric H. pylori infection and the presence of the bacteria in the oral cavity. A total of 443 dyspeptic patients participated in the study. Gastric H. pylori infection was detected by the rapid urease test and histology with Giemsa staining, PCR, or smear examination, whereas the presence of the bacteria in the oral cavity was observed by nested PCR from dental plaque. Relevant periodontal and dental parameters were recorded in the process of oral examination. Of the 443 study patients, oral H. pylori was found in the dental plaque of 263 (59.4%) and the stomach of 273 (61.6%). Additionally, in all four age groups, the prevalence of gastric infection was significantly higher among the patients with positive tests for H. pylori in their dental plaque than in the patients with no H. pylori in their dental plaque (P < 0.05). The oral cavity may be a potential reservoir for H. pylori, and the prevalence of oral H. pylori approximated that of gastric H. pylori in the studied population. Furthermore, a close relationship may exist between H. pylori in the oral cavity and bacteria in the stomach or gastric infection, and dyspeptic patients with gastric infection are more likely to harbor H. pylori in their oral cavity.