A patient with Münchhausen syndrome who had severe iron deficiency anemia (IDA) is reported. A 31 year-old female presented with irregular genital bleeding. However, gynecological examination disclosed no evidence of specific disorders causing bleeding. Tests for bleeding tendency and hemolysis were all negative. Although massive bleeding was absent, she had three episodes of a rapid fall in Hb level associated with marked fatigue and weakness, and subsequently rapidly developed serious IDA afterwards. Factitious bleeding was strongly suspected. Blood transfusion performed when the patient was not being watched failed to increase Hb, while transfusions given while the patient was watched were effective. She was not cooperative throughout the hospital course and was discharged on her own request. In outpatient clinic, the diagnosis was confirmed by the evidence that she diluted her own blood samples.