Objective: Over 50% of the world populations are infected with Helicobacter pylori (H. pylori). Most subjects are asymptomatic; however, in 1994, H. pylori has been categorized as group I carcinogen. The aim of the study was to investigate the relationship between H. pylori infection and gastric cancer. Methods: Thirty gastric cancer patients (GCs) and 30 gastritis patients were enrolled in the study. H. pylori was cultured on non-selective and selective medias, infection density was assessed by quantitative culture. Antibiotic sensitivity testing was performed. PCR was done for the H. pylori 16S rRNA gene in addition to cagA, vacA and iceA genes. Results: H. pylori could be cultured from 100% of specimens obtained from all patients. The density of H. pylori was higher in cancer cases than in gastritis patients. The 16S rRNA was detected in all GC patients (100%) while it was only detected in 70% of gastritis patients. The cagA gene was found in 53.3% vs 13.3% of GC and gastritis patients, respectively. The vacA gene was present in all GC patients (by at least one of its alleles) while it was only found in 33.3% of gastritis patients. The vacA s1m1 combination was the most predominant genotype in GC patients, while m2 was the commonest allele in gastritis patients (10%). The iceA gene was found in 86.7% vs 40% of GC and gastritis patients, respectively. Simultaneous presence of multiple H. pylori strains was proved, both phenotypically and genotypically. Conclusion: The development of GC is linked to infection with H. pylori harboring certain virulence genes. Higher infection density of H. pylori was found in GC patients. Co-existence of more than one strain of H. pylori in the same patient occurs in both malignant and benign lesions.