What are the possible complications of a sigmoidoscopy?

Complications: rare. Sigmoidoscopy is a very commonly done procedure with rare significant complications. Mild bleeding can occur in patients with hemorrhoids. Perforation of the colon wall can occur in less than 1/1000 patients, usually only in those with some type of pre-existing abnormality such as diverticulosis.
Sigmoidoscopy-NO!!! Perforation, bleeding infection amd death. Make sure it is done by a gastroenterologist. I have rarely done a sig. Any indication for a sig is an indication for a full colonoscopy. Doing just a sig may result in death from the biggest complication-missing a cancer. If your primary advises this, run.

Related Questions

What are possible complications of a flexible sigmoidoscopy?

Depends. If the test is done with sedation (typically not necessary) then there are risks of sedation. Otherwise typical risks of this procedure can include pain or cramps, bleeding (especially if there will be biopsies), infection, missing a lesion or a perforation (hole in the intestine). That being said, these risks are very rare.
Perforation. There are no common complications to flex sig. It is generally very safe. The two main risks is a missed lesion (15% rate) and a peroration (<1% rate).