To investigate Helicobacter pylori (H. pylori) infection in subjects with and without gastroduodenal diseases in Taiwan, IgG antibodies to H. pylori were examined in 136 healthy volunteers, 101 patients with non-ulcer dyspepsia, 122 gastric ulcers, 119 duodenal ulcers, and 161 gastric adenocarcinomas. The seropositivity was highest in duodenal ulcers (87.4%) (p < 0.001, as compared to healthy volunteers), followed by gastric ulcers (76.2%) (p < 0.01, as compared to healthy volunteers), but similar among gastric adenocarcinomas (60.3%), healthy volunteers (58.8%), and patients with non-ulcer dyspepsia (55.5%). Higher acquisition of H. pylori in younger patients with duodenal and gastric ulcers suggests a strong association with H. pylori. No ulcer characteristics, including number, location, and activity, were significantly statistically associated with the seropositivity of H. pylori in gastric and duodenal ulcers. Similarly, the location, extent of invasion, and histology of gastric adenocarcinoma was not significantly statistically associated with the seropositivity of H. pylori.