INTRODUCTION:A family history of gastric cancer (GC) is a well-known risk factor for GC. However, the association between family history of GC and the risk of GC and gastric adenoma according to the affected family members is unclear.METHODS:We analyzed the data of participants aged ≥40 years who underwent national GC screening between 2013 and 2014. Participants with and without a family history of GC among first-degree relatives were matched by age and sex in a 1:4 ratio.RESULTS:During a median follow-up of 4.9 years, 0.96% and 0.46% of 896,721 participants with a family history of GC and 0.65% and 0.32% of 3,586,884 participants without a family history of GC developed GC and gastric adenoma, respectively. A family history of GC among any first-degree relative was a risk factor for GC (adjusted hazard ratio [HR] 1.48, 95% confidence interval 1.45-1.52) and gastric adenoma (HR 1.44, 95% confidence interval 1.39-1.50). The HRs for GC and gastric adenoma were higher in participants with a family history of GC in parents and siblings (2.26 and 2.19, respectively) than in those with a family history of GC in parents only (1.40 and 1.41, respectively) or siblings only (1.59 and 1.47, respectively). The HRs for GC in participants with vs without a family history of GC were 1.62, 1.55, and 1.42 in the 40-49, 50-59, and ≥60 years' age groups of participants, respectively. Similarly, the HRs for gastric adenoma increased with decreasing age of participants.DISCUSSION:A family history of GC was a risk factor for both GC and gastric adenoma. The risk of GC and gastric adenoma of the participants was higher when both parents and siblings had GC.