Adult-onset Still's disease (AOSD) often presents with systemic multiple lymphadenopathy. In addition to the common paracortical and mixed patterns in AOSD lymph node histopathological features, other morphological patterns include diffuse, necrotic, and follicular patterns. However, to date, there have been few reports on the histopathological description of AOSD lymph nodes.An 18-year-old woman presented 2 months earlier with pain in her large joints with painless rash formation; bilateral posterior cervical lymph node, left supraclavicular lymph node, and left posterior axillary lymph node enlargement, and no tenderness. Left cervical lymph node resection was performed for pathological examination. The lymph node structure was basically preserved, and subcapsular and medullary sinus structures were observed. Many histiocytes in the sinus were observed, the cortical area was reduced, a few lymphoid follicles of different sizes were observed, and some atrophy and hyperplasia were noted. The lymphoid tissue in the paracortical region of the lymph node was diffusely proliferative and enlarged, mainly comprising 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 abundantly branching high endothelial small vessels with few scattered plasma cells and eosinophil infiltration. Lymphoid follicle immunophenotype with reactive proliferative changes was observed. Approximately 40% of the cells in the paracortical region were positive for Ki-67, and the histiocytes expressed CD68, CD163, and some expressed S-100, with the absence of myeloperoxidase. The immunoblasts expressed CD30 and CD20, not ALK or CD15. Background small- to medium-sized T cells expressed CD2, CD3, CD5, CD7, CD4, and CD8; the number of CD8-positive T cells was slightly predominant, and a small number of T cells expressed granzyme B and T-cell intracellular antigen 1. The patient received a comprehensive medical treatment after the operation, and her condition was stable without progression at the 11-month follow-up evaluation.The pathological features of AOSD lymphadenopathy raises the awareness of AOSD among pathologists and clinicians and aids in the diagnosis and differential diagnosis of AOSD lymphadenopathy from other reactive lymphadenopathies (lupus lymphadenitis, etc.) and lymphomas.© 2021. The Author(s).