Recurrent arthritis, fever and lymphadenopathy are symptoms of adult onset of Still's disease (AOSD). Differential diagnosis requires the exclusion of infections or malignant lymphomas. We report on a case of AOSD showing destructive lymphadenopathy, immunophenotyping of peripheral blood leucocytes revealed strong activation of T-lymphocytes. Bone marrow biopsy also showed an increase of lymphopoietic cells to 23%. Analysis of peripheral blood lymphocytes (PBL) after remission showed no remaining signs of activation. Analysis of lymphocyte activation by flow cytometry correlated with disease activity.