Endoscopic screening in 123 patients with pernicious anemia (PA) yielded 4 patients with solitary and 1 patient with multiple gastric carcinoid tumors. Quantitative histologic studies of multiple standardized biopsy specimens showed a significantly increased number of fundic mucosal argyrophil endocrine cells in 40 patients with PA when compared with 15 patients with simple fundic atrophic gastritis (p = 0.002) or 8 normal controls (p = 0.0001). Patients with simple atrophic gastritis had increased numbers of fundic mucosal argyrophil cells as compared with normal controls (p = 0.02). A significant difference was also noticed in the number of antral mucosal argyrophil cells between patients with PA and normal controls (p = 0.01), but not between patients with PA and patients with simple atrophic gastritis. It is concluded that, in addition to having hyperplasia of gastric mucosal argyrophil endocrine cells, patients with PA run an increased risk of developing gastric argyrophil cell carcinoid tumors, which should be regarded as potentially malignant.