Bilateral enlargement of both epididymes was observed in a 6-year-old German shepherd dog following a pre-scrotal urethrostomy. Testicular parenchyma showed regular structure, and the spermatogenesis and the steroidogenic functions were not modified. However, macroscopic examination of the tail and the body of both epididymes exhibited multiple white and well-delimited foci. Histopathological study of the epididymes confirmed the development of granulomas associated with extravasated spermatozoa. Urethrostomy caused a severe stenosis of the penile urethra, favouring the retention of urine at the urinary bladder. The retrograde pressure exerted by the distension of the urinary bladder could have allowed the urine to reach the prostatic urethra and the deferent ducts and, finally, the epididymes, causing irritation and rupture of the mucous layer of the epididymal duct, the consequent sperm extravasation and the development of sperm granulomas. We speculate that the inadequate surgical resolution of the urethral calculi caused the bladder distension, the subsequent retrograde flow of urine and the development of the lesions.