The aim of this study was to survey the occurrence of invasive group B streptococcus (GBS) disease in Norway and detect possible trends in characteristics of invasive GBS strains from 1996 to 2006. Data from national monitoring systems for infectious diseases in Norway were analysed. Of 638,452 live births in the period, 434 cases of invasive GBS disease in infants were reported. In adults and children older than 1 year of age, 969 cases were reported. The incidence of invasive GBS disease increased significantly in the elderly, while the incidence of neonatal early-onset disease was stable with 0.46 cases per 1,000 live births. The incidence of late-onset disease increased in 2005 and 2006. The lethality of GBS in infants increased from an average of 6.5% in 1996-2005 to 20% in 2006. Serotypes III and V were predominant in 839 invasive GBS strains characterized-type III in infants and type V in the elderly. The distribution of serotypes did not change throughout the period. The distribution of detected surface proteins was stable from 1996 to 2005, but the detection rates in types III and V were low. Molecular methods for GBS typing introduced in 2006 made characterization of nearly all strains possible and appear more applicable to epidemiological studies of GBS than conventional methods. Resistance to erythromycin and clindamycin increased significantly in 2006. The increased incidence in the elderly, the increased lethality in infants in 2006, and the increased resistance to erythromycin and clindamycin the same year might indicate changing characteristics of invasive GBS strains.