Primary gastric-carcinoma accounts for only 0.05% of pediatric gastrointestinal malignancies. Although elderly patients who have pernicious anemia are at greater risk of the development of atrophic gastritis and gastric carcinoma, pernicious anemia caused by vitamin B12 deficiency is extremely rare in otherwise healthy adolescents. The authors present a 14.5-year-old boy who had dimorphic anemia caused by vitamin B12 and iron deficiencies in whom atrophic gastritis and gastric carcinoma developed. To the best of our knowledge, this association has not been previously reported in children or adolescents.