The prevalence of group B streptococcal (GBS) colonization was studied in 136 pregnant women and their newborn infants by collecting vaginal and rectal swabs from the mothers and throat, rectal, and umbilical swabs from their infants. Maternal and infant colonization rates were 22% and 23%, respectively. One-third of infants born to colonized mothers and 15% of infants born to noncolonized mothers had GBS isolated. Of GBS-colonized infants, 50% remained colonized at the mean age of 2 months. Type V was the commonest serotype among GBS isolates from mothers and infants; type III strains were uncommon. The rarity of GBS disease in Gambian infants may be due to low rates of maternal carriage with the more virulent GBS serotypes.