Retained surgical sponges have been reported to occur after a diversity of surgical procedures, but transmural migration is a very unusual sequela. This article reports a case in which a retained surgical sponge eroded from the intra-abdominal space into the intestinal lumen, migrated distally, and spontaneously passed with defecation 12 weeks after the cesarean section. We performed a systematic review of the literature in Pubmed and found 64 cases of transmural migration of retained surgical sponges. Sixty-four cases have been reported of transmural migration, mainly after intra-abdominal surgery. The most frequent site of impaction is the intestine (75%), but we also found 2 cases that describe migration into the stomach and 7 into the bladder. Five more cases have been published describing transdiaphragmic migration. Only 4 cases describe a sponge spontaneously expelled through the rectum, whereas more than 93% needed re-intervention. We strongly advise only the use sponges with radiopaque markers during surgery and additional methodical wound/body cavity examination.