Rationale:Thrombotic thrombocytopenic purpura (TTP) with hemophagocytic lymphohistiocytosis (HLH) is very rare, and both of these rare blood diseases have high mortality. There have been few reports of 2 diseases being combined at the same time. We provide a rare case with a clear diagnosis, prolonging the patient's survival through aggressive treatment, providing clinicians with our experience in early diagnosis and early treatment of this disease.Patient concerns:A 56-year-old woman presented with a 1-month history of fever.Diagnoses:She was diagnosed with HLH due to elevated levels of ferritin and lactase dehydrogenase, which were confirmed by the presence of hemophagocytosis in the bone marrow. TTP was diagnosed based on the presence of symptoms characteristic of TTP and significantly low levels of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13).Interventions:Systemic corticosteroids and plasma exchange using 2 L of virus-inactivated frozen plasma per day were initiated as specific treatment.Outcomes:The patient’s consciousness improved posttreatment and platelets also increase gradually. In a follow-up after 1 month, the patient was generally well and without specific discomfort.Lessons:HLH patients themselves can have a significant reduction in platelet, as with TTP, it is very easy to misdiagnose or delay the diagnosis. How to diagnose early, actively find the primary disease, and treat it is crucial to improve the prognosis of HLH.