Rationale: Hemophagocytic lymphohistiocytosis (HLH) occurs primarily in pediatric population, or secondary to malignancy, infection, or autoimmune disease. This disease is rare and prognosis is generally poor. Only a small number of cases during pregnancy have been reported in literature. Patient concerns: We report a case of pregnancy-associated HLH secondary to natural killer (NK)/T cells lymphoma. She was admitted at 30 weeks and 3 days of pregnancy with complaints of abdominal pain and fever as high as 39.2 degrees C. The patient was found to have splenomegaly, pancytopenia, and acute hepatic failure. Diagnoses: A subsequent bone marrow biopsy revealed focal hemophagocytosis and atypical lymphoid cells. The splenic pulp also contained a large number of tissue cells proliferating and devouring mature red blood cells, lymphocytes, and cell debris. On the basis of these findings, we diagnosed the case as pregnancy-associated hemophagocytic lymphohistiocytosis secondary to NK/T cells lymphoma. Interventions: Treatment consisted with dexamethasone and etoposide in combination with rituximab. Outcomes: Due to timely termination of pregnancy, the neonate was in good condition. However, the patient died on the 18th day postoperation due to multiorgan failure. Lessons: We recommend that HLH be considered as differential diagnosis in a pregnant patient complaining of persistent fever, cytopenia, or declining clinical condition despite delivery of the baby. Prompt diagnosis and treatment is essential and fetal outcomes should also be considered. The decision to terminate a pregnancy and initiate chemotherapy during pregnancy with malignancyassociated HLH (M-HLH) needs to be further investigated in a larger cohort.