Group B Streptococcus (GBS) is the main etiological agent of neonatal sepsis in developed countries, however there is no detailed information on its incidence in Brazil. We registered the incidence and lethality of GBS infection in a Brazilian private maternity hospital from April 1991 to March 2000. Maternal risk factors contributing to neonatal infections were also scored. The rate of infection was determined by checking for GBS in the blood and liquor of symptomatic neonates within 72 hours of birth. Sepsis and/or early onset meningitis were diagnosed in 43 neonates (32 cases in blood, 1in liquor and 10 in blood and liquor). The overall incidence was 0.39 per thousand neonates and remained quite constant throughout the period, ranging from 0.25-0.63. Septic shock occurred in 33 neonates within 1 to 36 hours of birth (mean 15 hours). Among those patients, 26 (60%) died between the 5th and the 85th hour after birth. Maternal risk factors, according to CDC criteria, included: gestational age below 37 weeks in 26 cases (60%), amniorrhexis equal or superior to 18 hours in 7 cases (16%), and maternal temperature equal or superior to 38ºC in 4 cases (9%). None of the mothers had received prophylactic antibiotics during labor nor were urine, rectal or vaginal swabs screened for GBS. Although the incidence of GBS infection in the population in this study was lower than that found in developed countries, its rate of mortality was higher. The death rate could be reduced through recognition of the risk factors and prophylactic antibiotics during labor.