Objective: Demographic changes, associated with increased demands for open heart surgery in the elderly, place increased burden on financial resources. To evaluate perioperative risk factors affecting incidence of hospital events and estimation of hospital charges, 2577 patients greater than or equal to 65 years (range 65-91), operated on from January 1991 to December 1994, were compared with a concurrent cohort of 2642 younger patients. Methods: Statistical analysis, by surgical procedure, focused on hospital mortality, key postoperative complications affecting length of hospital stay and hospital charges. Results: Overall hospital mortality was 4.7%, 3.5% in younger patients Versus 6.1% in the older group (P much less than 0.01). Mortality was significantly lower in patients less than 65 years undergoing coronary artery bypass grafting (3% versus 5%, P < 0.01) and valve replacement (4% versus 9%, P = 0.01). Significant risk factors for hospital death in the elderly: diabetes (P < 0.01), hypertension (P < 0.01), myocardial infarction (P < 0.01) and congestive heart failure (P < 0.01). Significant postoperative events, more common in older patients, included prolonged ventilation (P much less than 0.01), congestive heart failure (P much less than 0.01), infection (P much less than 0.01), cerebrovascular accident (P < 0.01), and intra aortic balloon pump (P < 0.01). Incremental risk factors for morbidity in the elderly were: higher New York Heart Association class, congestive heart failure, emergent operation, and female gender. Mean length of hospital stay for the < 65 group was 15.3 versus > 19.5 days for the greater than or equal to 65 group (P much less than 0.01). Length of stay over Is days positively correlated with increased morbidity in both age groups. For patients greater than or equal to 65 years of age, the average hospital charge for open heart surgery was 172% higher for patients with a length of stay greater than 18 days compared with 165% for patients less than 65 years of age. Conclusions: Higher operative mortality and longer length of stay in elderly patients, resulting in increased health care costs, was associated with more co-morbidities. These results suggest interventions designed to reduce congestive heart failure and other co-morbidities may improve patient's recovery and reduce costs. (C) 1997 Elsevier Science B.V.