AIM:To investigate the outcome and effectiveness of two screening programs,National Cancer Screening Program(NCSP)and opportunistic screening(OS),for the detection of gastric cancer. METHODS:A total of 45 654 subjects underwent upper endoscopy as part of the NCSP or OS at the Chung-Ang University Healthcare System in Korea between January 2007 and December 2010.The study population was comprised of subjects over the age of 40 years.More specifically,subjects who took part in the NCSP were Medicaid recipients and beneficiaries of the National Health Insurance Corporation.Still photo-graphs from the endoscopies diagnosed as gastric cancer were reviewed by two experienced endoscopists. RESULTS:The mean age of the screened subjects was 55 years for men and 54 years for women.A total of 126 cases(0.28%)of gastric cancer were detected from both screening programs;100 cases(0.3%)from NCSP and in 26 cases(0.2%)from OS.The proportion of early gastric cancer(EGC)detected in NCSP was higher than that in OS(74.0%vs 53.8%,P=0.046). Among the 34 416 screenees in NCSP,6585(19.1%) underwent upper endoscopy every other year as scheduled.Among the 11 238 screenees in OS,3050(27.1%) underwent upper endoscopy at least once every two years during the study period.The detection rate of gastric cancer was found to be significantly higher during irregular follow-up than during regular follow-up in both screening programs(0.3%vs 0.2%,P=0.036).A higher incidence of EGC than advanced gastric cancer was observed during regular follow-up compared with irregular follow-up. CONCLUSION:Compliance to the screening program is more important than the type of screening system used. AIM: To investigate the outcome and effectiveness of two screening programs, National Cancer Screening Program (NCSP) and opportunistic screening (OS), for the detection of gastric cancer. METHODS: A total of 45 654 subjects underwent upper endoscopy as part of the NCSP or OS at the Chung-Ang University Healthcare System in Korea between January 2007 and December 2010. The study population was comprised of subjects over the age of 40 years. More specifically, subjects who took part in the NCSP were Medicaid recipients and beneficiaries of the National Health Insurance Corporation. Still photo-graphs from the endoscopies diagnosed as gastric cancer were reviewed by two experienced endoscopists. RESULTS: The mean age of the screened subjects was 55 years for men and 54 years for women. A total of 126 cases (0.28 % of of gastric cancer were detected from both screening programs; 100 cases (0.3%) from NCSP and in 26 cases (0.2%) from OS. proportion of early gastric cancer (EGC) detected in NCSP was higher than that in OS (74.0% vs 53.8%, P = 0.046). Among the 34 416 screenees in NCSP, 6585 (19.1%) underwent upper endoscopy every other year as scheduled. Amnon the 11 238 screenees in OS, 3050 (27.1%) underwent upper upper endoscopy at least once every two years during the study period. The detection rate of gastric cancer was found to be significantly higher during irregular follow-up than during regular follow-up in both screening programs (0.3% vs 0.2%, P = 0.036). A higher incidence of EGC than advanced gastric cancer was observed during regularly follow-up compared with irregular follow-up. CONCLUSION: Compliance to the screening program is more important than the type of screening system used.