This article uses Medicaid claims data to examine the adequacy of well-child care provided by different ambulatory care providers for selected children enrolled in Maryland Medicaid. Considerable provider variation was observed. The majority of the nearly one-quarter of the children with no well-child visits during the year appeared to have had no regular primary care source. Results contributed to the development of a managed care program designed to increase care accessibility and continuity and improve provider practices. Advantages and disadvantages of using claims data to investigate this public health issue care discussed.