A prospective study of post-operative morbidity in 258 elderly general surgical patients is reported. In 35% of patients no post-operative complications developed. Respiratory, wound and cardiac complications were the leading types of post-operative morbidity encountered, occurring in 39.5, 16.3, and 12.4% of patients, respectively. Life-threatening complications developed after surgery in 18.6% of patients, and the post-operative mortality rate (excluding 'non-viable' patients) was 5.8%. A statistical analysis of the effect of sex, age, urgency of surgery, type of surgery, and patient fitness on the pattern of post-operative morbidity revealed a number of significant associations which have not been previously identified in the elderly surgical patient.