Our objective was to examine the academic literature covering quality of childhood preventive care in the United States and to identify barriers that contribute to poor or disparate quality. We systematically reviewed articles related to childhood preventive care published from 1994 through 2003, focusing on 58 large observational studies and interventions addressing well-child visit frequency, developmental and psychosocial surveillance, disease screening, and anticipatory guidance. Although many children attend recommended well-child visits and receive comprehensive preventive care at those visits, many do not attend such visits. Estimates of children who attend all recommended visits range widely (from 37%-81%). In most studies, less than half is the proportion of children who receive developmental or psychosocial surveillance, adolescents who are asked about various health risks, children at risk for lead exposure who are screened, adolescents at risk for Chlamydia who are tested, or children and adolescents who receive anticipatory guidance on various topics. Major barriers include lack of insurance, lack of continuity with a clinician or place of care, lack of privacy for adolescents, lack of clinician awareness or skill, racial/ethnic barriers, language-related barriers, clinician and patient gender-related barriers, and lack of time. In summary, childhood preventive care quality is mixed, with large disparities among populations. Recent research has identified barriers that might be overcome through practice and policy interventions.