Hyperhemolysis is a life-threatening undesirable post-transfusion reaction characterized by a decrease in hemoglobin (Hb), hematocrit (Hct), reticulocytopenia and increase in ferritin concentration. It usually occurs in patients with hemoglobinopathies, rarely in people without genetic disorders of human red blood cells. The case concerns a 79-year-old woman who, due to a trophic ulcer and erysipelas, received one unit of kell positive packed red blood cells (pRBC). The patient did not exhibit symptoms of hypoxia despite the reduced value of hematological parameters (Hb: 10.4 g/dl, Hct: 31%). Delayed hemolytic transfusion reaction (DHTR) occurred after 11 days, with the presence of anti-K antibodies (Hb: 6.1 g/dl, Hct: 17%). Despite transfusion of three pRBC properly selected against patient’s antigens, only a transient increase in Hb and Hct was observed (Hb: 8.1 g/dl, Hct: 22%). These parameters rapidly decreased within 18 hours (Hb: 6.7 g/dl, Hct: 18%). The patient died due to circulatory and respiratory failure.