This article describes the high-cost and very high-cost patients in the fee-for-service medical plan of one of the nation's largest banks in terms of their demographics and medical plan expenses and utilization, within a single year and during a period of 4 consecutive years. High-cost patients ($5,000-25,000 annually) were dominated by older persons and women 20 to 39 years, while the very high-cost patients (at least $25,000) tended to be older men and infants of both genders. Very high-cost patients used 5 to 7 times more hospital patient days and visited with a physician on an outpatient basis twice as often as high-cost patients. In turn, the high-cost patients experienced 37 to 50 times as many patient days and twice as many outpatient visits as patients whose annual expenses were below $5,000. Longitudinal analyses suggested that while most of the high-cost patients are typically low-cost patients or nonusers of services who experience high-cost time spans, some of them suffer from more serious chronic health problems and are apt to become very high-cost patients. Focusing case-management interventions on this small subgroup of high-cost patients may prevent some very high-cost cases in the future.