The growth of a large population of people without permanent housing in the United States has brought with it the necessity to address the unmet health needs of this group. As homelessness spreads, its demographic pattern has become more heterogeneous, with young vulnerable families now the major subgroup. This paper explores issues of homelessness in Westchester County, N.Y., which, despite being the 10th richest county in the United States, has the highest per capita homeless rate in the state. Children younger than age 18 represent the majority of this group. Barriers to the delivery of health care services are described, including fragmented life-styles, lack of insurance, insensitivity of care givers, distance from services, and inflexibility of traditional sources of health care. A model that has been developed for delivery of services is discussed. This model, the Outreach Health Care Unit, is run by nurse practitioners in collaboration with family physicians and is centered at the site of social service activities for homeless families and single men in Yonkers, N.Y. It is a collaborative endeavor of a nursing school, community hospital family practice residency program, and a network of social service agencies. The use of this model for education and research is also discussed since the goal is to provide both health services and training for health care providers.