Postpartum vaginal cystic lesions constitute a common situation that is caused either by inflammation or by accumulation of lymph. We report a case of a 33-year-old woman who had bilateral duplication of the pelvicalyceal system and ureter, and after the labor of her second child, she had one ureter prolapse into the vagina after initially appearing as a cystic lesion. Ureteral duplication is the most common renal abnormality, occurring in approximately 1% of the population and in 10% of children who are diagnosed with urinary tract infections. In our case we consider possible that this clinical situation was a result of a combination of postpartum pelvic floor trauma and prolapse of the ureter. There are only several of these cases in the literature where ureter prolapse is associated and complicated by pelvic floor trauma caused during or after labor. The clinical approach of the cystic lesions located in the vagina during the postpartum period should include a meticulous examination of the urinary system before any other medical practice.