Purpose: This study aimed to analyze the effect of screening by using endoscopy on the diagnosis and treatment of gastric cancer. Materials and Methods: The clinicopathologic characteristics of gastric cancer were compared in individuals who underwent an endoscopy because of symptoms (non-screening group) or for screening purposes (screening group). The distributions of gastric cancer stages and treatment modalities in 2006 and 2011 were compared. Results: The proportion of patients in the screening group increased from 45.1% in 2006 to 65.4% in 2011 (P<0.001). The proportion of stage I cancers in the entire patient sample also increased (from 60.5% in 2006 to 70.6% in 2011; P=0.029). In 2011, the percentages of patients with cancer stages I, II, III, and IV were 79.9%, 8.2%, 10.9%, and 1.1%, respectively, in the screening group, and 47.9%, 10.8%, 29.8%, and 11.5%, respectively, in the non-screening group. The proportion of laparoscopic and robotic surgeries increased from 9.6% in 2006 to 48.3% in 2011 (P<0.001), and endoscopic submucosal dissection increased from 9.8% in 2006 to 19.1% 2011 (P<0.001). Conclusions: The proportion of patients diagnosed with gastric cancer by using the screening program increased between 2006 and 2011. This increase was associated with a high proportion of early-stage cancer diagnoses and increased use of minimally invasive treatments.