• Age \>6 months and ≤80 years at the beginning of the index MAS episode.

• Diagnosis of Still's disease (sJIA or AOSD diagnosis).

• Diagnosis of MAS according to treating physician in the medical record.

• Patients who have received at least 3 consecutive days of GC after diagnosis of MAS and/or are judged by the Investigator to be refractory to GC due to clinical worsening of patient's condition.

• The onset of the index MAS episode occurred between 01 January 2012 and 30 September 2022.

• According to local regulations, waivers of consent will be sought for study participants from the appropriate regulatory authorities and/or the independent ethics committee (IEC)/institutional review board (IRB). o For patients not covered by waivers of consent, signed, and dated informed consent provided by the patient, or the patient's legally authorized representative(s) for patients under the legal age (with patient assent, as applicable) or who have died, should be obtained before any study-related activities are undertaken.