Introduction: Group B Streptococcus (GBS) is the leading cause of neonatal infections, but its role in infections among children and adults in France remains to be assessed. Methods: The clinical circumstances of GBS isolation, the serotypes involved, and the antibiotic susceptibility of the strains were evaluated with the assistance of a network of 29 laboratories. Results: 66.4% of the isolated GBS strains were derived from specimens collected from adults and children. Bacteremia occurs in 84.8% of cases in individuals over 50 years of age. GBS serotype III predominates among strains isolated from neonatal infections (66.6%). In adults and children, the majority of isolated GBS strains are serotype I (32.7%) and III (35.9%). All GBS strains are susceptible to penicillins and cefotaxime. Resistance to tetracyclines is notable (79.4%). The prevalence of erythromycin resistance (20.9%) is higher for strains isolated from newborns (>30%) than for those isolated from children and adults (17.4%) and for GBS serotype V (46.9%). Discussion-Conclusion ¿ The different serotypes of GBS exhibit a certain specificity regarding anatomical site. The use of erythromycin for the prophylaxis or treatment of GBS infections warrants further discussion. (R.A.)