Minoia et al reported the MS score for the macrophage activation syndrome (MAS) in a patient with systemic juvenile idiopathic arthritis (sJIA). This can help to distinguish MAS from active sJIA. The authors are from the Pediatric Rheumatology International Trials Organization, the Childhood Arthitis & Rheumatology Research Alliance, the Pediatric Rheumatology Collaborative Study Group and the Histiocyte Society.