peer reviewed ; Background: Group B Streptococci cause invasive disease in neonates, pregnant women and non-pregnant adults. In the last decades capsular serotypes (type) Ia, Ib, II and III caused the majority of clinical diseases. More recently, in North America, type V emerged as the more common type in non-pregnant adults with invasive disease. Methods: From January 1999 through December 2001, we received and typed a total of 334 clinically significant strains of GBS isolated in the laboratories belonging to the Belgian network for epidemiological surveillance. 113 were recovered from neonates blood or cerebrospinal fluid (92 early onset EOD, 21 late onset LOD), 14 were isolated from pregnant women with severe infections and 204 were recovered from adults with invasive disease. From the same laboratories, during the first trimester of 2002, 302 isolates from pregnant women were also typed (max. 5 isolates /lab.) Results: In neonatal EOD type III was the more common (41,3%) followed by II (19.6%), Ia (16.3%), Ib (13%), V (8.7%) and IV (1.1%), whereas type III caused the majority (85.7%) of LOD cases. In adults, all types were well represented except type IV: 20.3% Ia, 12.7% Ib, 13.1% II, 23.1% III, 2.7% IV, 19% V and 9% remained non typeable (NT). In colonized pregnant women, all types were also well represented except type IV: 25.5% Ia, 13.3% Ib, 14.9% II, 17.7% III, 5% IV, 15.5% V and 8.1% remained NT. Type III was more frequently the cause of EOD than a colonizing strain during pregnancy and in contrast NT isolates did not cause EOD (P<0.001) Conclusions: 1) Type III was still the major type in neonatal infections in Belgium. 2) Type distribution of GBS differed by age-group of patients 3) Type V belonged to the 3 more represented types in adults 4) Compared to colonizing GBS in pregnant women, distribution of types causing EOD was different.