Streptococcus pyogenes, or group A streptococcus (GAS), is a rare cause of nosocomial infection. In France in 2002, it was isolated in 0.3% of nosocomial bacteremias. The case fatality rate for invasive GAS infections ranges from 10% to 70%, depending on whether or not toxic shock syndrome is present. The impact of these infections could be limited by measures aimed at preventing the transmission of streptococci in the hospital setting. Invasive GAS infections fall under the mandatory reporting of nosocomial infections, due to the rare and specific nature of the causative pathogen and, potentially, in the event of the patient’s death (Decree No. 2001-671 of July 26, 2001). The authors describe reported cases of invasive Group A streptococcal nosocomial infections occurring in the postoperative or postpartum period between August 1, 2001, and December 31, 2003, in France, along with their investigation and prevention strategies.