Background: Both iron deficiency and iron deficiency anemia require extensive investigation because of their possible association with gastrointestinal malignancy. If no other sources of blood loss are apparent, the gastrointestinal tract is examined to detect sources of occult blood loss. In the absence of gastrointestinal symptoms, the colon is first examined, especially in the elderly. The aim of this study was to determine the outcome of esophagogastroduodenoscopy (EGD) after a prior negative colonoscopy in outpatients without gastrointestinal complaints, referred due to iron deficiency anemia. Methods: Thirty-five patients (22 female and 13 male) with a median age of 71 years were studied over a 2-year period. Anemia was defined as a hemoglobin (Hb) level below 7.4 mmol/l in women or below 8.0 mmol/l in men and iron deficiency if one of the following was present: ferritin level equal to or below 20 µg/l for men and equal to or below 10 µg/l for women, a serum iron concentration equal to or below 45 µg/dl (8.1 µmol/l) with a transferrin saturation of 10% or less, or the absence of iron stores in bone marrow biopsy specimens. Patients with prior gastrointestinal disease or surgery, gastrointestinal symptoms, or other obvious causes of blood loss were excluded. Lesions that were considered to be potential sources of blood loss were clearly defined. Results: The mean Hb level of the 35 patients studied was 5.5 mmol/l (range 1.8-7.8 mmol/l). Abnormalities were found in 10 patients (28.6%), all of which were benign. Erosive and ulcerative lesions in the stomach, in a hiatal hernia, or in the esophagus were diagnosed in eight patients, benign villous adenoma was seen in one patient, and celiac disease in another, although duodenal biopsies were taken in only 15 patients. Erosions and/or ulcerations were found in four of 11 patients (36%) using NSAIDs and/or salicylates (ASA). Seventy percent of the lesions were found in elderly patients (>65 years), 56% of whom were using NSAIDs and/or ASA. Conclusions: EGD should always be performed in patients with iron deficiency anemia after a negative colonoscopy, although upper gastrointestinal malignancy will probably be an infrequent finding. The presence of a significant, treatable lesion is most likely in the elderly and in those with a history of NSAID or ASA use. Routine duodenal biopsies should be performed to further increase the outcome of EGD.