Background: Adult-onset Still's disease (AOSD), which presents many non-specific symptoms, such as rash leukocytosis, spiking fever, and sore throat, is a rare auto inflammatory disease. Other clinical features that are frequently observed include lymphadenopathy, arthralgia, serositis, splenomegaly, and hepatomegaly. Laboratory tests show high levels of C-reactive protein, ferritin, and erythrocyte sedimentation rate reflecting the systemic inflammatory process in AOSD patients. Case presentation: The patient was a middle-aged woman with a high fever (39.8 C), sore throat, rashes on limbs with pruritus, mainly at the joints (elbow, knee, and ankle), muscle aches, dizziness, infirmity, weakness, and poor appetite without arthralgia. The ferritin level was above 1500 (normal value: 14-233) ng/L. Antineutrophil, antinuclear antibodies, and rheumatoid factor were negative. Combining the symptoms such as fever, rash, stress-induced acute inflammation, arthritis, and ferritin levels, the patient was eventually diagnosed with adult Still's disease. She received methylprednisolone 40mg intravenously every 12 hours for one week. On the second week, the dose was reduced to 40mg in the morning and 20mg in the evening, and finally, the dose was reduced to 40mg oral intake in the morning and 8mg in the evening. After half a month of treatment, the patient's high fever and skin rashes subsided, and the other symptoms also gradually relieved. Conclusions: A case of a middle-aged woman diagnosed with adult Still's disease is reported, and the possible pathogenesis and treatment of the disease are discussed. This case highlights the importance of early diagnosis and timely treatment of adult Still's disease to prevent potentially fatal complications.