Cost characteristics of hospital patients were analyzed in 2238 medical records randomly selected from 42,880 dicharges in six contrasting hospital populations in the year 1976. Total hospital billings were concentrated on a few patients. On average, the high-cost 13% of patients consumed as many resources as the low-cost 87%. Repeated hospitalizations for the same disease were more characteristic of the expensive patients than were single cost-intensive stays, "intensive care," or prolonged single hospitalizations. Potentially harmful personal habits (e.g., drinking and smoking) were indicated in the records of high-cost patients substantially more often than in those of low-cost patients. Unexpected complications during treatment were five times more frequent in the high-cost group. Public policy programs for health insurance or cost control should include provisions based on the special characteristics of high-cost patients.