We report a case of multifocal urothelial carcinoma in situ of the left ureter with early stromal invasion and concomitant in situ lesions in bladder, prostate and seminal vesicle. After complete topographical mapping of the cystoprostatovesiculectomy specimen the unusual manifestation of urothelial carcinoma in situ in a seminal vesicle turned out to be a tumour spread via the ductus ejaculatorius into the seminal vesicle. DNA sequencing of the tumour suppressor gene TP53 of different tumour lesions revealed identical wild-type sequences.