Pyoderma gangrenosum received this name due to the notion that this disease was related to infections caused by bacteria in the genus Streptococcus. In contrast to this initial assumption, today the disease is thought to have an autoimmune origin. Necrotizing fasciitis was first mentioned around the fifth century AD, being referred to as a complication of erysipelas. It is a disease characterized by severe, rapidly progressing soft tissue infection, which causes necrosis of the subcutaneous tissue and the fascia. On the third day of hospitalization after antecubital venipuncture, a 59-year-old woman presented an erythematous and painful pustular lesion that quickly evolved into extensive ulceration circumvented by an erythematous halo and accompanied by toxemia. One of the proposed etiologies was necrotizing fasciitis. The microbiological results were all negative, while the histopathological analysis showed epidermal necrosis and inflammatory infiltrate composed predominantly of dermal neutrophils. Pyoderma gangrenosum was considered as a diagnosis. After 30 days, the patient was discharged with oral prednisone (60 mg/day), and the patient had complete healing of the initial injury in less than two months. This case was an unexpected event in the course of the hospitalization which was diagnosed as pyoderma gangrenosum associated with myelodysplastic syndrome.