Group A streptococci cause a wide range of illnesses from non-invasive disease such as pharyngitis to more severe invasive infections such as necrotising fasciitis. There remains uncertainty about the risk of invasive disease among close contacts of an index case of invasive disease and whether this risk warrants antibiotic prophylaxis. A 19-200 fold increased risk among household contacts has been reported in the literature. Recommendations for antibiotic prophylaxis regimens vary by country. A comprehensive literature review together with preliminary analysis of 2003 United Kingdom data from the strep-EURO programme informed the interim recommendations of an expert working group. The evidence base to formulate definitive guidance is weak. Risk calculations based on provisional UK data estimated that over 2,000 contacts would need to receive antibiotic prophylaxis to prevent a subsequent case of invasive group A streptococcal disease. The Working Group considered that currently available evidence did not warrant the routine administration of chemoprophylaxis to all close community contacts. More robust risk estimates will be derived from ongoing UK surveillance data to inform a review of this guidance in 2005.