Necrotizing fasciitis (NF) is an infection of the deep soft tissues that results in progressive destruction of the muscle fascia and overlying subcutaneous fat. These infections can be sudden, vicious, and fast-spreading. If not treated quickly with antibiotics and debridement of the infected tissue, the patient may develop septic shock, which may lead to multiple organ failure and death. NF is difficult to early diagnose due to the overlying tissue can appear unaffected initially. We report an unusual case of NF of the buttock and left thigh that clinically mimics lumbar disc herniation. This patient was successfully treated with emergent fasciotomy and intensive care. We recommend that patients with low back pain and unilateral leg pain should be diagnosed carefully especially keeping NF in differential diagnosis.