We herein report a case of ectopic prostatic tissue in the retrotrigone of the bladder. A 35-year-old man was referred to our hospital because of bladder tumor which was incidentally discovered on abdominal ultrasonography (US). US and computed tomography (CT) showed a tumor in the bladder wall 1.5 cm in diameter. Magnetic resonance imaging (MRI) revealed an invasive bladder tumor. Cystoscopy showed a non-papillary, wide-based tumor in the retrotrigone of the bladder. Transurethral resection of bladder tumor was carried out and pathological findings showed ectopic prostatic tissue. This is the 8th case of ectopic prostatic tissue in the Japanese literature.