The authors present two cases of necrotizing fasciitis (NF), one case of dermatomyositis and one case of posttraumatic muscle injury, which have similar magnetic resonance imaging findings in terms of skin, subcutaneous fat, superficial and deep fasciae and muscle involvement. These cases highlight the need for cautious interpretation of magnetic resonance imaging (MRI) findings, for they are nonspecific and the preoperative decision should be based mostly on the evolution of the clinical status.