Objective: To determine the risk of nasopharyngeal (NP) carriage of penicillin-resistant S. pneumoniae associated with use ofβ-lactam antibiotics and child care center (CCC) attendance in young children. Study Population: 343 children aged 6 weeks to 5 years receiving health care at a large pediaric practice with sites in Norfolk and Chesapeake, VA who were enrolled during the first 9 months (3/96-11/96) of an ongoing 3-year surveillance study. Methods: Attempts were made to contact parents of all age-eligible children. Demographic, medical, and out-of-home child care information on the family were collected at enrollment. Antimicrobial use in study children in the 6 months prior to culture was asertained from pediatric office records. NP specimens obtained from study children were tested for S. pneumoniae by P disc, and minimum inhibitory concentrations of penicillin were determined by E test (susceptible<1, intermediate.1-1.5, high ≥2). Results: Penicillin-resistant S. pneumoniae were identified in 33 of 343(9.6%) children; 23 (6.7%) were intermediate and 10 (2.9%) were highly resistant. Among 33 children colonized with resistant S. pneumoniae. 14 (42%) received ≥2 courses of β-lactam antibiotics in the prior 6 months compared with 61 of 310 (20%) children without resistant S. pneumoniae (P=.006, Fishers Exact). Resistant S. pneumoniae were identified in 5 of 28 (18%) children attending CCC ≥6 hours per week compared with 28 of 315 (9%) children attending child care homes, other child care programs, or cared for at home (p=.17). The risk for penicillin resistance among children who received ≥2 courses of β-lactam antibiotics was greater than 3 times the risk found in children who had received one course or no β-lactam antibiotics (OR=3.0; 95% CI, 1.4-6.3). The risk for carriage of penicillin-resistant S. pneumoniae associated with ≥2 courses of β-lactam antibiotics was more than 2-fold higher among children attending CCC (OR=6.2; 95% CI, 0.60-65) than among those not attending CCC (OR=2.5; 95% CI, 1.1-5.8). Conclusions: Colonization with penicillin-resistant S. pneumoniae in young children was associated with frequent use ofβ-lactam antibiotics. CCC attendance appeared to increase the risk, possibly as a result of greater exposure to resistant pathogens in CCCs.