Introduction: Primary hemophagocytic lymphohistiocytosis (HLH) is a hyper-inflammatory disorder characterized by dysregulation of inflammatory cells and cytokine signaling. Although first-line treatment consisting of immunosuppressive therapy and allogeneic hematopoietic cell transplantation (HCT) is often curative, it remains unknown whether any effective therapies exist for disease relapse/progression after HCT. Case Presentation: Here we present a case of a 29-year-old male with primary HLH who failed HLH-94 protocol and subsequently underwent myeloablative HCT. Disease relapse occurred at 9 months following HCT, and donor lymphocyte infusion (DLI) was initiated as salvage therapy. The patient subsequently achieved durable long-term disease-free survival following a DLI, without significant treatment-related complications. Conclusion: To our knowledge, this represents the first case demonstrating the efficacy of DLI for relapsed primary HLH.