Infection with the Gram-negative bacterium Helicobacter pylori leads to different clinical and pathological outcomes in humans, including chronic gastritis, peptic ulcer disease and adenocarcinoma of the stomach. H. pylori-induced damage to gastric mucosal cells is controlled by bacterial virulence factors encoded by genes of the cag pathogenicity island, which trigger the inflammatory response of the host through the activation of nuclear factor kappaB-dependent gene transcription. Also, H. pylori infection impairs the processes of gastric mucosal healing through inhibition of epidermal growth factor receptor-dependent signal transduction pathways and induction of apoptosis. H. pylori infection may influence the progression from chronic gastritis to gastric adenocarcinoma by stimulating cell proliferation and growth factor expression, inhibiting apoptosis and increasing the DNA mutation rate of infected gastric mucosa.