Unexplained cytopenias can be related to bone marrow necrosis (BMN) in critically ill patients as it can be encountered in several diseases or life-threatening conditions. We present the case of a 39-year-old woman with pancytopenia revealing a BMN in the setting of an acute pyelonephritis with septic shock, multiple organ failure and sickle cell trait. After a short review on the subject, we suggest that various haematological abnormalities occurring in critically ill patients may be related to a mild to severe marrow necrosis.