Haemophagocytic lymphohistiocytosis (HLH) is a rare syndrome characterized by fever and cytopenia due to phagocytosis of erythrocytes, leukocytes, platelets, and their precursors in bone marrow and other tissues. HLH can be primary (genetic) or associated with neoplastic diseases, autoimmune diseases or infections. HLH is a rare syndrome but can cause very severe illness, and if unrecognized/untreated the condition is associated with a high mortality. We present two cases of cytomegalovirus infection-associated HLH in patients with inflammatory bowel disease during azathioprin treatment.