A 77-year-old woman with rheumatoid arthritis was admitted as an emergency because of pain in the right leg with purpura. She was diagnosed with severe cellulitis and sepsis and started on intravenous antibiotics; however, the lesion rapidly extended to the proximal thigh and she died only 38 h after the onset of the first symptom. Autopsy and tissue culture revealed necrotizing fasciitis caused by Streptococcus dysgalactiae subspecies equisimilis. Physicians should consider that necrotizing fasciitis may be present when soft-tissue disorder is suspected in patients receiving corticosteroid therapy, which is associated with tissue fragility and immunosuppression.