The course of severe invasive group A β-hemolytic streptococcal (GABHS) infections is often precipitous, requiring prompt diagnosis and rapid initiation of appropriate therapy. Therefore, physicians must have a high index of suspicion of this disease, particularly in patients at increased risk (eg, those with varicella or diabetes mellitus). Although a relationship between the use of nonsteroidal antiinflammatory drugs and severe invasive GABHS infections has been suggested, at present data on which to base a clinical decision about the use or restriction of nonsteroidal antiinflammatory drugs in children with varicella are insufficient. When necrotizing fasciitis is suspected, prompt surgical drainage, debridement, fasciotomy, or amputation often is necessary. Many experts recommend intravenously administered penicillin G and clindamycin for the treatment of invasive GABHS infections on the basis of animal studies. Some evidence exists that intravenous immunoglobulin given in addition to appropriate antimicrobial and surgical therapy may be beneficial. Although chemoprophylaxis for household contacts of persons with invasive GABHS infections has been considered by some experts, the limited available data indicate that the risk of secondary cases is low (2.9 per 1000) and data about the effectiveness of any drug are insufficient to make recommendations. Because of the low risk of secondary cases of invasive GABHS infections in schools or child care facilities, chemoprophylaxis is not indicated in these settings. Routine immunization of all healthy children against varicella is recommended and is an effective means to decrease the risk of invasive GABHS infections.