An infected paraprostatic cyst originating from the prostate parenchyma was diagnosed in a seven-year-old male American Staffordshire terrier with dysuria. The diagnosis was based on the history, the clinical and ultrasonographic findings, bacteriological culture, extensive histopathological examination and a DNA-test. Treatment consisted of the surgical removal of a great part of the cyst and the omentalization of the remnant, castration and antibiotic therapy. Immunohistochemistry demonstrated an urothelial lining of the cyst. A DNA-test excluded persistent Mullerian duct syndrome (PMDS). The cyst had an open connection with the urethra and probably originated from an embryonic remnant located in the prostatic gland. The dog had a prosperous recovery but the dysuria and urinary incontinence persisted. At four months postoperatively, a new paraprostatic cyst was diagnosed by ultrasound. Aspiration of its content revealed infected urine
