BACKGROUND: Vitamim B12 deficinecy is not a common disease and the causes and clinical findings were not clearly documented in Korea so far. Concerning that vitamin B12 deficiency caused by gastrectomy is not uncommon, we analysized the causes of vitamin B12 deficiency and clinical findings. METHODS: We reviewed the clinical records of cases diagnosed as vitamine B12 deficiency megaloblastic anemia in Hallym Medical Center from July, 1992 to Octorber, 2004. RESULTS: Forty five cases were included. Twenty five cases were performed gastrectomy and 8 cases had pernicious anemia, however the causes of 10 cases with vitamin B12 deficiency were not clear. The rate of the cases induced by gastrectomy were increased after 2001 compared with the rate before this point. Six cases were combined with iron deficient anemia. In five of the 6 cases who were combined with iron deficient anemia, the MCV and MCH were not increased. Forty three cases had anemia and anemia-associated symptoms such as dyspnea and weakness. Some of the cases complained diarrhea, numbness, or ataxia. CONCLUSION: We found that the gastrectomy was the dominant cause of vitamin B12 deficient megaloblastic anemia in this study. We suggest that vitamin B12 deficient megaloblastic anemia should be considered in follow-up of the cases of gastrectomy.