To determine the incidence and time sequence of mortality and major morbidity after ambulatory surgery. Prospective outcome survey of patients at 16 to 72 hours and 30 days after their surgical procedures. A tertiary care rural referral center providing ambulatory care. A total of 38,598 patients aged 18 years and older undergoing 45,090 consecutive ambulatory procedures and anesthetics. Contact rates for 72 hours and 30 days were 99.94% and 95.9%, respectively. Mortality and major morbidity incidences, including myocardial infarction, central nervous system deficit, pulmonary embolism, and respiratory failure. Thirty-three patients either experienced major morbidity or died (1:1366 [proportional risk]). Four patients died (1:11,273), two of myocardial infarction and two in automobile accidents. No patient died of a medical complication within 1 week of surgery. Of the 31 patients who developed a major morbidity (1:1455), 14 (45%) had myocardial infarction (1:3220), seven (23%) had a central nervous system deficit (1:6441), five (16%) had pulmonary embolism (1:9018), and five (16%) had respiratory failure (1:9018). Four events (13%) occurred within 8 hours of surgery (1:11,273), 15 (48%) in the next 40 hours (1:3006), and 12 (39%) in the next 28 days (1:3758). In this ambulatory surgical population, more than one third of major morbidity occurred 48 hours or later after surgery. Overall morbidity and mortality rates, however, were very low.