Hemophagocytic lymphohistiocytosis (HLH) is a rare group of disorders of immune dysregulation characterized by clinical symptoms of severe inflammation. There are basically two types of clinical scenarios: Familial HLH and sporadic HLH. It is thought that the syndrome is implicated in the development of infections, malignancies, and autoimmune diseases. HLH, whether primary or secondary, is characterized by activated macrophages in hematopoietic organs, hepatosplenomegaly, cytopenia, and fever; however, HLH complicated with polyserositis (PS) has never been reported.We present a case of fever in a 46-year-old previously healthy Chinese woman complicated by pericardial, pleural, and abdomen effusions. She had no contact with sick individuals, recent travel, illicit drug use, or new sexual contacts. She did not consume alcohol or tobacco and lacked a family history of other diseases. Antibiotics were prescribed for suspected infection, and acute liver injury subsequently occurred. Contrast-enhanced computed tomography showed mild pericardial effusion, pleural effusion, hepatosplenomegaly, and a large amount of ascites. A full blood count revealed leukopenia and thrombocytopenia. Increased ferritin and triglyceride levels were observed. The test for Epstein-Barr (EB) virus DNA was positive. This suggests that EB virus replication and EB virus infection existed. Additional studies showed hemophagocytosis in bone marrow biopsy specimens. The patient's condition progressed rapidly. After providing symptomatic support treatment, eliminating immune stimuli, and administering comprehensive cyclosporine and dexamethasone treatment, the patient's condition continued to progress, and the patient's family members decided to stop treatment; the patient subsequently died.This case shows the significance of considering HLH as part of the evaluation of unexplained fever and PS of unknown origin.