Necrotizing fasciitis is a rare soft tissue infection characterized by a rapidly spreading infection of the subcutaneous tissue. Early diagnosis is important as it requires immediate and complete debridement of infected tissues and antibiotic therapy. Necrotizing fasciitis usually involves the extremities, abdomen, and groin, but rarely involves the head and neck. Necrotizing fasciitis has an aggressive course; however, in rare cases, it can present in a subacute indolent form which can be misdiagnosed as other cutaneous diseases. Our case is a unique presentation of subacute necrotizing fasciitis of the posterior neck, which was initially diagnosed as a herpes zoster infection, in a patient with undiagnosed diabetes mellitus, which was complicated with diabetic ketoacidosis and sepsis.