This clinical lesson, based on two case histories, illustrates a complication seen after manipulation of the rectal wall in patients who have undergone radiotherapy for localised prostate cancer. Rectal bleeding, which is feared by patients, can be the first sign of radiation proctitis. Manipulation of the rectal wall, for example by taking biopsies or Argon plasma coagulation, should be done with caution and only if absolutely necessary, because it can lead to fistula formation.