Background and aim: HER2 is considered to have prognostic value in gastric cancer and test for HER2 overexpression help to select patients for targeted therapy with trastuzumab. The authors aim to study endoscopic and histopathological characteristics of gastric adenocarcinoma and their relationship with HER2 overexpression. Patients and methods: Biopsy samples from 64 gastric cancer patients were examined for HER2 status by immunohistochemical staining. Results: On Lauren classification, 42.2 percent were intestinal type and 57.8 percent were diffuse type. On WHO classification, 43.8 percent were tubular adenocarcinoma, 7.8 percent were mucinous adenocarcinoma, 17.2 percent were signet-ring cell carcinoma, and 31.3 percent were undifferentiated carcinoma. 29.7 percent were well-differentiated, 18.8 percent were moderately-differentiated, and 51.6 percent were poorly-differentiated carcinoma. HER2 was positive in 23.5 percent of gastric carcinomas, 40 percent cardia tumors and 22 percent non-cardia tumors. HER2 positivity among polypoid, fungating, ulcerated, and infiltrative types were 30.8 percent, 37 percent, 6.3 percent and 0 percent, respectively. HER2 overexpression in intestinal type was higher than that in diffuse type (37 percent vs. 13.5 percent, p = 0.04). HER2 overexpression in tubular adenocarcinoma, mucinous adenocarcinoma, signet-ring cell carcinoma, and undifferentiated carcinoma was 35.7 percent, 9.1 percent, 20 percent and 15 percent, respectively. 36.8 percent of well-differentiated tumors, 33.3 percent moderately-differentiated tumors, and 12.1 percent of poorly-differentiated tumors were found to be HER2-positive. Conclusions: HER2 overexpression was found in 23.5 percent of gastric carcinoma and was associated with its endoscopic findings and histopathologic types.