A 16-year-old male patient who was on oral iron treatment for iron deficiency anemia for the last one year was seen at the Haematology clinic with complaints of weakness, pallor, and jaundice. A complete blood count revealed Hb of 4.2 mmol/L, Hct of 0.14, and MCV of 76 fl. A blood smear showed 50% neutrophils, 40% lymphocytes, and 10% monocytes with anisocytosis, poikilocytosis, polichromasia in erythrocytes and normoblasts. Reticulocyte count was under 1%. There was a slight erythroid hyperplasia in the bone marrow aspiration. Biochemical examinations showed total bilirubin of 3.9 mg/dL, indirect bilirubin of 3.4 mg/dL, and lactate dehydrogenase (LDH) of 6085 U/L (220-450). In re-evaluating the history of the patient, he was seen to be complaining of dark discoloration of morning urine. Perl's reaction was found to be positive for hemosiderin in the urine sediment. Because Ham's test was positive, the levels of CD55, 58, and 59 proteins on erythrocyte membranes were found to be lower. The patient was started 32 mg of methylprednisolone and his anaemia was improved by the $14^th$ day of treatment. When evaluating iron deficiency anemia resistant to iron supplementation, PNH should be kept in mind.