Necrotizing fasciitis associated to group A streptococcus (S. pyogenes) infection is a deep-seated infection of the subcutaneous tissue that results in progressive destruction of fascia and fat, with a high mortality rate due to a rapid progression of the illness to shock and multiple organ dysfunction. The challenge is to perform a prompt diagnosis because it is often confused with a minor soft-tissue infection. This infection should be aggressively treated with systemic antimicrobials, surgical debridement, and critical care. We present two cases of necrotizing fasciitis associated to infection with Streptococcus pyogenes patients developed myonecrosis and toxic shock syndrome within the following 24 hours after admission. In addition, we reviewed the pathogenic mechanism, diagnosis and treatment of this syndrome and discuss published treatment recommendations.