The use of a hospital-based primary care clinic for health maintenance and illness care and use of the emergency room were monitored for 3 years for 293 children who had been enrolled in the clinic as infants. Infrequent users of one facet of care were infrequent users of other facets of care, and they remained so for all 3 years. The same trends were noted for frequent users. Children who used the clinic for health maintenance infrequently were more likely to have registered in the clinic after 2 months of age and to demonstrate consistently infrequent use throughout the 3 years. Children who used the clinic for illness care infrequently were more likely to have at least two siblings and to demonstrate consistently infrequent use. Children who used the emergency room infrequently were likely to have been consistently infrequent users for emergencies and illness throughout the 3 years. Conversely, those who used the clinic frequently for health maintenance were more likely to have registered before 1 month of age, to have multiple chronic conditions, and to demonstrate consistently frequent use for maintenance throughout the 3 years. Frequent users for illness care were more likely to have none or one sibling, multiple chronic conditions, and to demonstrate consistently frequent use for illnesses. Finally, children who used the emergency room frequently were likely to have multiple chronic conditions and to demonstrate sustained frequent use throughout the 3 years. These results suggest that patterns of use are established as early as the first year of life.