Diseases caused by Streptococcus pneumoniae are diverse and common, with an incidence in Europe of nearly 800 per 100,000 people. They affect both children and adults, although the incidence is higher at the extremes of the age spectrum. These bacteria are naturally susceptible to many antibiotics; however, since the first strain of penicillin G-susceptibility-reduced pneumococcus (PSDP) was described in Australia in 1967, numerous studies have shown an increase in antibiotic resistance, particularly to beta-lactams. Data published in France show a continuous increase in PSDP (55.4% in 2001), particularly among children, where the rate reaches 71%, though with significant variation by region. Since 1995, the Regional Pneumococcal Surveillance Networks (ORP), consisting of a network of laboratories spread throughout France, have been monitoring serogroups and the evolution of antibiotic resistance in isolated strains every two years. Since 1999, this surveillance has focused exclusively on strains isolated from cerebrospinal fluid (CSF), blood cultures, and pus from acute otitis media (AOM). Since 2001, a partnership between the ORPs and the Pneumococcal Reference Center (CNRP) has enabled the serotyping of the majority of strains, which is essential for evaluating the impact of the new heptavalent Prevenar® vaccine. In 2003, the ORPs and the CNRP continued this surveillance in partnership with the French Institute for Public Health Surveillance (InVS); the results are presented in this report in comparison with those from 2001. (Introduction)