The rate of Streptococcus pneumoniae carriage among adults was compared with that among children (age, < or =6 years) in the same population. Nasopharyngeal culture results for 1300 adults and 404 children were analyzed. S. pneumoniae was carried by only 4% of the adults, compared with 53% of children in the same community. Young age, day care center attendance, having young siblings, and no antibiotic use during the month before screening were associated with the high carriage rate among children, whereas the only risk factor associated with carriage among adults was the presence of a respiratory infection on the screening day. S. pneumoniae serotype distribution and antibiotic resistance patterns differed between adults and children. Isolates of the same serotype--even of the same clone--differed in their antibiotic susceptibility patterns between children and adults. In a subanalysis of 151 pairs of children and their parents and of 32 pairs of siblings, intrafamilial transmission of S. pneumoniae could not be demonstrated.