Necrotizing fasciitis is a severe infection that leads to necrosis of the tissues and systemic involvement, with a rapid progress and a fatal outcome. Although this condition is rare, it must be suspected and rapidly treated, as the prognosis depends on this. The treatment is based on immediate surgery, wide spectrum antibiotic treatment, and support measures in a critical care unit. We present the case of a patient who was admitted to Recovery room after surgical debridement due to suspicion of fasciitis. The patient also had a common variable immunodeficiency or hypogammaglobulinaemia, characterised by a B lymphocyte deficiency, as well as on treatment with methotrexate for Crohn's disease. Both produced an immune deficiency. After 11 days of treatment there was a clinical, analytical and haemodynamic improvement, and she was discharged.