Ten patients developed apnea or cardiopulmonary arrest during or following endoscopy in more than 10,000 consecutive endoscopies. These complications occurred in patients over the age of 60 years with many associated diseases. Four of the reactions occurred close to the time of giving intravenous medication, the majority after the stimulation of the procedure had ended, usually more than 30 min after the last dose of medication. The initial 7,500 procedures were conducted without automated monitoring, but the most recent 2,500 procedures employed finger pulse oximetry. Monitoring has not prevented apnea and cardiopulmonary arrest, but it provides earlier recognition.