Undesired side effects and complications of gastrointestinal endoscopy and premedication are rare events. However, this is true only of endoscopic units with experienced investigators, modern equipment and monitoring. The complication rate of upper gastrointestinal endoscopy is about 0.1% with cardiopulmonary events predominating. The typical complication of colonoscopy is perforation, seen in 0.2%. The relevant ERCP specific complication is acute pancreatitis in about 1%, followed by acute cholangitis. The most serious complications of laparoscopy are hemorrhage from the liver biopsy site, bleeding from abdominal wall varices, and perforation of the colon. The cardiopulmonary mortality is low for upper gastrointestinal endoscopy as well as for colonoscopy (1 death/20,000 procedures). Premedication, chronic obstructive pulmonary disease, coronary heart disease, valvular heart disease and, last but not least, advanced age, must be considered risk factors for the development of complications of gastrointestinal endoscopy. Balanced indication, particularly in the elderly patient, should be the consequence. If possible, endoscopy should be performed without sedatives. If premedication is necessary, it should be used sparingly. Not only patients at high risk for the development of cardiopulmonary complications, but all patients undergoing endoscopy must be carefully monitored after premedication, during and after endoscopy. The non-invasive procedure of pulse-oximetry is appropriate for continuous monitoring of arterial oxygen saturation in patients with cardiopulmonary diseases, irrespective of their premedication status. Antibiotic prophylaxis is recommended in patients with valvular heart disease or prosthetic valves. Standardized cleaning and disinfection of the instruments is of great importance to avoid hepatitis B or HIV transfer.(ABSTRACT TRUNCATED AT 250 WORDS)