The patient, a 56-year-old man, had surgery for anal fistula at the age of 28. In August 2007, he underwent a radical retropubic prostatectomy (RRP) for prostate cancer. Rectal injury was not recognized during the operation. However, on the 8th postoperative day, fecaluria appeared, and rectourethral fistula was diagnosed. We attempted conservative therapy including diverting colostomy and continued drainage using a urethral catheter. Subsequently, the fistula closed spontaneously 3 months after RRP. Eight months after RRP, we performed a transanal repair of rectal mucosa based on the rectal wall advancement flap procedure. The postoperative course was uneventful, and the colostomy was closed in July 2008. By April 2009, he had normal voiding and full anal continence without fistula recurrence.