Two female cases are descibed. In one case of a 25‑year‑old vegan with heavy menstruations, the main cause of iron deficiency anemia was a stomach cancer, whose delayed diagnosis contributed to treatment failure and death. In the 2nd case, of a 60‑year‑old female, the cause of iron deficiency anemia was chronic bleeding from gastrointestinal tract caused by diffused large B cell lymphoma localized in the small intestine, a location difficult to access by standard gastro‑and colonoscopy. The patient underwent standard immunochemotherapy and remains in complete remission. In conclusion, iron deficiency anemia, particulary if persisting longer, should result in intensive diagnostic procedures aimed at exclusion/confirmation neoplastic disease as the main cause.