A prospective study was carried out on 288 general surgical patients aged 65 years and over. Over 40% of patients suffered no post-operative complication. The commonest post-operative problem was respiratory, with 17% of patients having simple atelectasis, 12% acute bronchitis and 10% pneumonia. Six per cent of patients developed post-operative heart failure and/or myocardial infarction. Delirium was noted post-operatively in 7% of patients, and new focal neurological signs in 1%. The post-operative hospital fatality rate was 5% (4% when deaths due to carcinomatosis were excluded). Nine patients out of ten spent less than a month in hospital. The relation of post-operative morbidity and mortality to seven factors was examined: type of surgery, urgency of surgery, urgency of admission, age, number of pre-operative medical diagnoses, American Society of Anesthetists' grade, and pre-operative mobility level. It appears that pre-operative medical fitness rather than chronological age is the main determinant of post-operative outcome in the elderly surgical patient.