In an effort to provide medical care that is both more effective and less costly, the new variants of managed care organizations have instituted a variety of incentives and administrative controls that impact on the types and quantity of care provided to patients. Evidence suggests that the early forms of managed care, namely prepaid group practices, showed particular promise in improving the primary care delivered to children, ie, care that is accessible, person-focused in the long term, comprehensive, coordinated, and oriented toward achieving better outcomes. However, recent evidence concerning the quality of care delivered to children in the newer variants of managed care is mixed and scant; the newer organizational forms may not facilitate and may even have a negative impact on the attainment of primary care. Managed care can have a positive effect on first contact care, because it contractually defines a primary care provider and reduces use of the emergency room as a source of care. It may, however, have mixed effects on other aspects of access and use, depending on the plan's particular characteristics. Longitudinality is threatened by the disruption of prior relationships with out-of-plan providers and by the instability of both enrollees and providers in managed care plans. Children's benefits in managed care arrangements tend to include more preventive services, but access to specialty services has generally been found to be more restrictive. Coordination of care is not inherent to managed care, and many plans are no more likely to foster communication than are traditional indemnity plans. Evidence for the superior clinical quality afforded to children by new variants of managed care is lacking. Because managed care arrangements are proliferating rapidly, better studies are needed to prove or refute the contention that managed care has a significant positive effect on quality of care.