AbstractNecrotizing fasciitis is a rare, but potentially fatal bacterial infection of the soft tissues. Establishing the diagnosis at the early stages of the disease remains the greatest challenge. We report a case ofnecrotizing fasciitis involving the upper extremity. Sonography revealed subcutaneous emphysema spreading along the deep fascia, swelling, and increased echogenicity of the overlying fatty tissue with interlacing fluid collections. The patient responded well to early surgical debridement and parenteral antibiotics. © 2010 Wiley Periodicals, Inc. J Clin Ultrasound, 2011