Rectal tears were detected in three horses treated for colic. Based on historical, clinical, and postmortem findings, the tears could not be attributed to the attending veterinarian and were therefore not iatrogenic (physician induced). One tear was attributable to an infarction that presumably resulted from thromboembolism; 1 tear occurred without any evidence of external cause and resulted in such severe peritonitis that the cause and resulted in such severe peritonitis that the cause could not be determined, and 1 tear occurred during rectal palpation by the owner, before he called the veterinarian. Postmortem examination of the last horse revealed lesions suggestive of thromboembolism. It was concluded that thromboembolism may have caused or predisposed to two of the rectal tears and could not be ruled out in the third.