Hemophagocytic lymphohistiocytosis (HLH) is a severe, life-threatening hyperinflammatory syndrome characterized by dysregulated activation of cytotoxic T-lymphocytes and macrophages, with lymphoma-associated HLH (LA-HLH) carrying a particularly poor prognosis due to delayed diagnosis and lack of optimal treatment regimens. While the systemic features of LA-HLH—such as persistent fever, pancytopenia, and hepatosplenomegaly—are well-documented, its oral manifestations have not been previously described in the literature. We herein report a case of LA-HLH in a 28-year-old female patient who presented with intermittent fever along with recurrent oral ulcers. The patient had been diagnosed with ENKTL (non-nasal type, stage IVB, PINK-E 4, high risk) two years prior, with skin and muscle involvement, and had achieved remission after chemotherapy and autologous hematopoietic stem cell transplantation. A comprehensive diagnostic workup, including bone marrow biopsy and laboratory assessments, confirmed the diagnosis of LA-HLH secondary to relapsed extranodal NK/T-cell lymphoma (non-nasal type, stage IVB). The oral lesions were managed with Kangfuxin mouthwashes, while the underlying lymphoma and HLH were treated with dexamethasone and etoposide, combined with chidamide and tislelizumab. To the best of our knowledge, this is the first report documenting oral mucosal involvement by ENKTL occurring in a patient with LA-HLH. These oral lesions, as a manifestation of localized lymphoma progression, may serve as early clinical clues to lymphoma relapse with secondary HLH, rather than being a specific early sign of LA-HLH itself. Increased awareness of these potential oral findings among clinicians and dentists could facilitate earlier diagnosis of lymphoma relapse in LA-HLH patients and improve the multidisciplinary management of associated complications.