Three male children are reported with similar histories and clinical findings. They were born with imperforate anus which was corrected in the newborn period by a combined abdominal perineal pull-through procedure, plus ligation and transection of a fistula connecting the rectum with the midposterior urethra. Postoperatively, they were found to have a cyst-like structure behind the prostate which communicated through a narrow neck with the midposterior urethra. Histologically, the wall of the pouch was composed mainly of a muscular coat which was lined internally by rectal mucosa in 2 patients and by rectal and urogenic mucosa in the other patient. Because of their anatomic relationship and microscopic features, these cystic structures are thought to represent the stumps of the original rectourethral fistulae which have failed to obliterate and then progressively enlarged. The failure of obliteration and subsequent enlargement of these fistulous stumps were probably precipitated by the more distal urethral obstruction, organic in one patient, functional in the other two. An additional factor which may be incriminated, but which cannot be substantiated in view of incomplete data available on the original surgical procedure, is that too long a fistulous tract was left behind at the time of the surgical correction of the imperforate anus.