Macrophage activation syndrome (MAS) is a severe and life-threatening complication of rheumatic diseases in childhood. It is most associated with systemic juvenile idiopathic arthritis (sJIA). We present the case of a nine-year-old boy diagnosed with sJIA for six years who developed MAS triggered by hepatitis A. He was managed with anakinra and corticosteroids. Some of the clinical features of MAS occur late in the disease course, so clinicians should keep a high index of suspicion to initiate treatment early. This case highlights that anakinra and corticosteroid use in treating MAS is effective and has a good safety profile for pediatric patients.