The major risks are pain, bleeding, or infection. For gastrointestinal endoscopy, there is also a risk of perforation (tearing) of the intestinal wall.
Reactions to the anesthesia can occur (though they are rare). For this reason your breathing, blood pressure, heart rate, and oxygen level will be monitored during the procedure.
Endoscopies also can be used to perform treatment procedures. For example, bleeding from lesions can be stopped, and colon polyps can be removed.
During endoscopic ultrasound, a needle may be inserted into the area of interest, in order to take a sample of cells. This is called fine needle aspiration.