Objectives: To measure prevalence of Staphylococcus aureus colonization in household contacts of children with acute S aureus skin and soft tissue infections (SSTI), determine risk factors for S aureus colonization in household contacts, and assess anatomic sites of S aureus colonization in patients and household contacts. Design: Cross-sectional study. Setting: St Louis Children's Hospital Emergency Department and ambulatory wound center and 9 community pediatric practices affiliated with a practice-based research network. Participants: Patients with community-associated S aureus SSTI and S aureus colonization (in the nose, axilla, and/or inguinal folds) and their household contacts. Outcome Measures: Colonization of household contacts of pediatric patients with S aureus colonization and SSTI. Results: Of 183 index patients, 112 (61%) were colonized with methicillin-resistant S aureus (MRSA); 54 (30%), with methicillin-sensitive S aureus (MSSA); and 17 (9%), with both MRSA and MSSA. Of 609 household contacts, 323 (53%) were colonized with S aureus: 115 (19%) with MRSA, 195 (32%) with MSSA, and 13 (2%) with both. Parents were more likely than other household contacts to be colonized with MRSA (odds ratio, 1.72; 95% CI, 1.12 to 2.63). Methicillin-resistant S aureus colonized the inguinal folds more frequently than MSSA (odds ratio, 1.67; 95% CI, 1.16 to 2.41), and MSSA colonized the nose more frequently thanMRSA(odds ratio, 1.75; 95% CI, 1.19 to 2.56). Conclusions: Household contacts of children with S aureus SSTI had a high rate of MRSA colonization compared with the general population. The inguinal fold is a prominent site of MRSA colonization, which may be an important consideration for active surveillance programs in hospitals.