Background: Adult onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder that often presents with systemic multiple lymphadenopathy. In addition to the common paracortical and mixed patterns in AOSD lymph nodes histopathological features, the other morphological patterns include diffuse, necrotic, and follicular patterns. However, there have been very few reports to date on the histopathological description of AOSD lymph nodes.Case presentation: An 18-year-old female presented two months earlier with pain in her large joints with painless rash formation, bilateral posterior cervical lymph nodes, left supraclavicular lymph nodes and left posterior axillary lymph nodes enlargement, and no tenderness. Left cervical lymph node resection was performed for pathological examination. Histologically, lymph node structure is basically preserved, subcapsular sinus, medullary sinus structure exists, there is a lot of histiocytes in the sinus, cortical area is reduced, a few lymphoid follicles of different sizes can be seen, some atrophy, some hyperplasia. The lymphoid tissue in the paracortical region of the lymph node was diffusely proliferative and enlarged, mainly composed of histiocytes with abundant cytoplasm, immunoblasts, and numerous lymphocytes with slightly irregular small to medium-sized nuclei. Nuclear karyorrhexis was easily observed, showing a few nuclear debris and the “starry sky” phenomenon, accompanied by abundant branching high endothelial small vessels with a background of scattered few plasma cells and eosinophil infiltration. Immunohistochemically, lymphoid follicle immunophenotype with reactive proliferative changes. About 40% of the cells in the paracortical region were positive for Ki-67, and the histiocytes expressed CD68, CD163, some expressed S-100, and no MPO. The immunoblasts expressed CD30, CD20, and not ALK or CD15. Background small to medium-sized T cells express CD2, CD3, CD5, CD7, CD4, and CD8, the number of CD8 positive T cells is slightly predominant, and a small number of T cells express GRB and TIA-1. The patient received comprehensive medical treatment after operation, and the condition was stable without progression at the 11-month follow-up evaluation.Conclusion: The presentation of morphologic cases of AOSD lymphadenopathy will increase the awareness of AOSD among pathologists and clinicians, and aid in the diagnosis and differential diagnosis of AOSD lymphadenopathy from other reactive lymphadenopathies and lymphomas.