OBJECTIVES: To present Baltimore City Health Department's (BCHD) experience in developing and operating an ombudsprogram for Maryland's Medicaid Managed Care HealthChoice Program as an innovative public health response to its MCH Title V assurance functions. METHODS: This paper presents a case study that 1) describes Baltimore City's Consumer Ombudsman and Assistance Program (COAP) in terms of development, function, structure, and resources; 2) provides a summary of its first 30 months' experiences, both quantitatively and qualitatively; and 3) describes COAP's successes, value, and limitations with respect to its three essential roles--a) conflict resolution for individuals, b) education for consumers, providers and advocates, and c) catalyst for quality improvement. OUTCOMES: Over 1300 cases (involving enrollment, access, billing, and treatment issues) were referred to COAP by the State's Complaint Resolution Section during the first 2 1/2 years of HealthChoice. Ombudsman interventions resulted in conflict resolution for enrollees using a continuum of education, mediation and advocacy, and in generating systematic data for systems change through collaboration with state and community public health, managed care organization, provider, consumer, and advocacy officials and groups. CONCLUSIONS: Public health ombudsprograms can effectively assist and educate enrollees; and provide concurrent, or real-time, information for consumer, provider, health plan, and advocacy groups, as well as public policymakers and legislators to better inform systems improvement and innovation. The community-based ombudsman role is an effective mechanism to ensure appropriate care for MCH populations and others with special needs. Such efforts can be funded by federal/state Medicaid administrative funds and are a sound investment in assuring access to comprehensive care for vulnerable populations.