Background Almost half of the world’s population suffer from the Helicobacter pylori (H. pylori) infection, but only some individuals develop gastric diseases with clinical symptoms. One reason for the phenomenon may be the different pathogenicity of infected H. pylori strains. The presence of cytotoxin-associated gene A (cagA) and expression of vacuolating cytotoxin activity encoded by vacuolating cytotoxin gene A (vacA) are considered the two major virulent markers of H. pylori. The aim of this study was to detect dominant cagA/vacA genotypes and coinfection frequency of H. pylori in patients with peptic ulceration (PU) or chronic gastritis (CG), and to determine correlations among different cagA/vacA genotypes, coinfection and severity of the diseases. Methods For each of 139 patients in Zhejiang Province who had been diagnosed as PU or CG based on clinical symptoms and gastroscopy, two gastric biopsy specimens (one from antrum and the other from corpus) for H. pylori isolation were taken by two diff Background Almost half of the world’s population suffer from the Helicobacter pylori (H. pylori) infection, but only some individuals develop gastric diseases with clinical symptoms. One reason for the phenomenon may be the different pathogenicity of infected H. pylori strains. The presence of cytotoxin-associated gene A (cagA) and expression of vacuolating cytotoxin activity encoded by vacuolating cytotoxin gene A (vacA) are considered the two major virulent markers of H. pylori. The aim of this study was to detect dominant cagA / vacA genotypes and coinfection frequency of H. pylori in patients with peptic ulceration (PU) or chronic gastritis (CG), and to determine correlations among different cagA / vacA genotypes, coinfection and severity of the diseases. Methods For each of 139 patients in Zhejiang Province who had been diagnosed as PU or CG based on clinical symptoms and gastroscopy, two gastric biopsy specimens (one from antrum and the other from corpus) for H. pylori isolation we re taken by two diff