BACKGROUND: To prepare for national introduction of a pneumococcal conjugate vaccine of restricted valency, we studied nasopharyngeal carriage of Streptococcus pneumoniae in Gambian infants. METHODS: We studied 236 infants in 21 villages. We collected nasopharyngeal swab samples at birth, twice per month for 6 months, and every second month until 1 year of age. We studied time to acquisition and duration of pneumococcal carriage according to serotype. RESULTS: All infants carried S. pneumoniae at some point. Sixty-five serotypes were found, and the 5 most common serotypes (6B, 19F, 6A, 14, and 23F) accounted for 51% of isolates. The mean age at first acquisition of carriage was 33 days (95% confidence interval, 29-36 days). There were no significant differences in acquisition rates between the 6 most common serotypes (P = .067) or between vaccine serotypes, vaccine-related serotypes, or nonvaccine serotypes (P = .317). However, the duration of carriage differed significantly between the 6 most common serotypes (P = .004). The rate of reacquisition of carriage and the duration of carriage did not differ significantly between the 6 most common serotypes (P = .229 and P = .669 respectively). However, nonvaccine types were acquired faster (P = .004) and were carried for a shorter duration (P < .001) than were vaccine serotypes. A previous episode of serotype 14 carriage was associated with delayed reacquisition of this serotype (P = .005) and longer duration of carriage (P = .017). CONCLUSIONS: The data provided in this study regarding time to acquisition and duration of pneumococcal carriage in Gambian infants provide an important baseline for evaluating the impact of the introduction of a pneumococcal conjugate vaccine in The Gambia and elsewhere in Africa.