Health officials planned a stepped care system (regionalized) for Tlalpan, in the Federal District of Mexico (D.F.), to address problems of duplicated services, inappropriate use of available resources, increasing costs of medical care, and unmet health needs in the population. Cross-sectional surveys were carried out in the community, in health centers and in hospital based ambulatory services (outpatient department and emergency department) to obtain current, specific and valid information about need and utilization patterns. Users of the various services differed from each other and from the community by age, educational level, occupation, rights to prepaid care and utilization patterns. Emergency department users came back for care repeatedly and sought preventive services from the emergency department. Major reasons for attending the emergency department included respiratory and gastrointestinal problems, plus poisonings, accidents, and complications of pregnancy. Outpatient department users arrived without referral from medical sources and continued to return frequently for care. Users were mostly adults, particularly older adults, with problems of a more chronic nature, e.g. nervous system problems, genitourinary problems, etc. The health centers attended clients from the designated area of influence who had referred themselves to the center for care. Children were the most frequent clients with acute, common problems, e.g. diarrhea and respiratory problems. Health maintenance activities were assessed for which children received the most complete coverage, but some women lacked the necessary care for perinatal health and family planning. In general, health centers seemed to be functioning appropriately, although the magnitude of unattended need in their areas of influence must be investigated further. Specific indicators identified deviations from the patterns of use expected in a stepped care system for the outpatient and emergency departments indicating directions for change in the administrative policies of the services.