X-linked agammaglobulinemia is a common type of primary immunodeficiency disorder that's caused by mutation of the BTK gene. The absence of B lymphocytes and plasma cells causes recurrent infections. Patients with X-linked agammaglobulinemia also have a high risk for developing hematological malignancies and, to a lesser degree, carcinoma. We report here on a 26-years-old male patient who suffered with X-linked agammaglobulinemia that was caused by BTK gene mutation, and he developed a gastric cancer in the antrum. He was noted to have chronic atrophic gastritis and diffuse intestinal metaplasia on the endoscopic examination that was done 7 years previously. We recommend regular esophagogastroduodenoscopic evaluation for a patient with X-linked agammaglobulinemia in order to make an early diagnosis of stomach carcinoma.