An approach is presented for estimating the need for specific types of services within a system of care for children and adolescents with serious emotional disturbances and for estimating the staff, dollars, and other resources required. Many of the issues that need to be resolved before one can "size" and cost out a system of care are also explored, such as defining the service area; defining the target population; determining how many will be served; and defining values and the organization of services. The estimating method described was used by the District of Columbia (D.C.) in its 1985-86 child mental health planning process and was adapted from a model in use in South Carolina. The method is applied to several types of services, including: outpatient services; therapeutic nursery programs; psychoeducational programs; therapeutic foster care; in-home crisis intervention services; therapeutic group homes; supervised independent living; residential treatment facilities; acute inpatient services; and case management services. For each type of service, information provided includes: South Carolina's estimate; D.C.'s rationale for adjusting it; and D.C.'s method for determining the amount of resources required. Appendixes contain a definition of the target population, a continuum of services and values, a framework of cost breakdowns, inpatient bed needs assessment, and intensive case management criteria. (35 references) (JDD)