This study identified consistently high and low users of medical care services in a group of older HMO members continuously enrolled for six years. Consistently high users made up 26% of the sample, but accounted for more than 50% of total outpatient contacts and hospital admissions. Average ambulatory care costs were more than four times greater for the high users compared with the low users. Consistently high users were older than consistently low users, but did not differ significantly in other sociodemographic characteristics. Compared with the low users, the high users reported more total medical conditions and were more likely to indicate they had arthritis, high blood pressure, heart conditions, and other chronic problems. They perceived themselves to be in poorer health and reported higher levels of psychologic distress. The low users tended to be less satisfied, but the two user groups were not significantly different regarding use of services outside the HMO.