Complications of upper gastrointestinal endoscopy are uncommon. Approximately one complication occurs with every 1000 procedures. The mortality rate is estimated to be between 0.5 and 3 per 10,000 cases. Cardiopulmonary events comprise 50% of all major complications, and most of these events result from the medications used for conscious sedation. Diagnosis, treatment, and prevention of common complications are discussed; rare complications are mentioned.