Necrotizing fasciitis (NF) is a rare, life-threatening soft-tissue infection and a medical and surgical emergency, with increasing incidence in the last few years. It is characterized by a rapidly spreading, progressive necrosis of the deep fascia and subcutaneous tissue. Necrotizing fasciitis is often underestimated because of the lack of specific clinical findings in the initial stages of the disease. Many adjuncts such as laboratory findings, bedside tests--e.g., the "finger test" or biopsy--and imaging tests have been described as being helpful in the early recognition of the disease. Imaging is very useful to confirm the diagnosis, but also to assess the extent of the disorder, the potential surgical planning, and the detection of underlying etiologies. The presence of gas within the necrotized fasciae is characteristic, but may be lacking. The main finding is thickening of the deep fasciae due to fluid accumulation and reactive hyperemia, best seen on magnetic resonance imaging.