A 66-year-old patient was seen at the emergency department with a skin infection of the left leg, probably erysipelas, which worsened despite the use of antibiotics. The symptoms had started 5 days earlier. The patient was respiratory and haemodynamically stable, he was not clinically ill and had relatively little pain. Lab tests revealed leucocytosis, significantly elevated CRP values and signs of renal and hepatic impairment. The patient was admitted because of suspected necrotising soft tissue infection (NSTI). The diagnosis was confirmed in the operating room. Eventually the lower leg had to be amputated. This case shows that NSTIs do not always have to run a fulminant course. There are also subacute forms, which are only rarely described in the literature. However, in case of subacute skin conditions, NSTIs are low on or even absent from the list of considerations for differential diagnosis, while early diagnosis is necessary for reducing mortality associated with this disease.