Necrotizing fasciitis (NF) is a medical-surgical emergency characterized by severe bacterial infection that affects the subcutaneous tissue and spreads to the underlying fascia; usually it is caused by penetrating trauma, sometimes by surgical therapy, very rarely by minor insults such as insect bites. Systemic lupus erythematosus (SLE) is a potentially fatal autoimmune disease involving virtually all the key components of the immune system. Although cases of post-infection autoimmunity were already described, a literature search using Pub Med and Medline revealed that SLE was never reported to occur in patients affected, immediately before, with NF. We observed and herein report, however, a case of a woman showing an insect-bite-induced NF, which was immediately followed by the development of a SLE. In conclusion, this case of postinfection autoimmunity provides early evidence of a patient developing SLE immediately after NF, and suggests that caution in the follow-up of NF is necessary, because NF might favor the development of a severe autoimmunity.