Group B streptococcal infection may result in significant morbidity and mortality in both infants and adults. The experience with group B streptococcal disease was analyzed at one medical center over a ten-year period from 1975 to 1984. Streptococcus agalactiae bacteremia was observed in 29 adults and 26 infants, with an attack rate of 0.2 cases per 1000 adult admissions and 3.2 cases per 1000 live births, respectively. The majority of adult infections apparently occurred as a result of nosocomial acquisition and was associated with a high mortality rate of 38%. Risk factors for group B streptococcal sepsis in adults include diabetes mellitus, malignancy, and hepatic failure. The majority (73%) of neonatal cases occurred within seven days of birth and occurred in a setting of maternal fever, prolonged rupture of membranes, or prematurity. The mortality rate in infants was remarkably low at only 15%. Fatalities occurred in both adults and infants, despite appropriate antimicrobial therapy. Infection control strategies against group B streptococcus must address potential nosocomial dissemination in adults as well as vertical transmission in infants.