In-hospital outcomes and cost were examined among 2,272 elderly patients (> or =75 years) and 9,745 younger patients (<75 years) who underwent coronary artery bypass graft surgery at 5 United States and 4 Canadian hospitals. Hospital course and cost data were obtained from a resource and cost accounting system used by each of the 9 hospitals. Compared with younger patients, elderly patients had longer hospital stays, increased in-hospital mortality, and increased costs. After controlling for clinical differences, age > or =75 years was associated with an increase in cost of 11%. Given the aging North American population, these results have important implications for health care planning for the next several decades.