Background/Aims: A positive family history is an increased risk factor for gastric cancer within family members. This study examined the prevalence of H. pylori infection, serum antibodies to CagA and VacA, and atrophic gastritis and/or intestinal metaplasia in the relatives of gastric cancer patients. Methods: A total of 726 subjects included 300 relatives of 300 separate gastric cancer patients and 426 controls. All subjects underwent upper gastrointestinal endoscopic examination with a rapid urease test. Blood samples were obtained to test for the presence of serum antibodies to the CagA and VacA proteins of H. pylori. Results: The prevalence of H. pylori infection was higher in relatives of cancer patients(75.3%) than in controls(60.1%), and the adjusted odds ratio was 2.1 (95% CI, 1.52.9). There was no specific relationship between CagA and VacA, and H. pylori infection. Atrophic gastritis and/or intestinal metaplasia were found more frequently found in H. pylori-infected relatives of cancer patients(26.1%) than in H. pylori-infected controls(12.9%). Conclusions: These results strongly support a role for H. pylori infection in familial aggregation of gastric cancer. The prophylactic eradication of H. pylori infection in the offspring or siblings of gastric cancer patients may be clinically beneficial. (Korean J Helicobacter Res Prac 2002;2:170-177)