During the 11-year period 1975 through 1985, seven hundred ninety-five patients 90 years of age and older underwent operative procedures at the Mayo Clinic, Rochester, Minn. Overall serious morbidity within 48 hours after surgery was 9.4%, and the mortality was 1.6%. The 30-day, 1-year, and 5-year mortality rates were 8.4%, 31.4%, and 78.8%, respectively. Short-term morbidity and both short- and long-term mortality were highly associated with the American Society of Anesthesiologists physical status classification of the patient. Emergency procedures carried a significantly higher risk for morbidity and mortality within the 48-hour period and, to a lesser extent, for long-term mortality. Overall, poorer patient survival was associated with higher American Society of Anesthesiologists class; male sex; preoperative renal, liver, and central nervous system impairment; and surgery on the mouth, nose, or pharynx. When compared with age-, sex-, and calendar year--matched peers from the general population, there was a modest decrease in patient survival at 1 year that reversed by 2 years, with observed survival at 5 years comparable to the rate expected.