In this presentation, a case of cystic adenocarcinoma of the prostate in a 13-year-old Terrier male dog is described pathologically. The patient was brought to the Selcuk University Veterinary Faculty animal hospital with complaints of cross-walking for two months, urinary incontinence and paralysis in the last two days. After the physical examination, the total prostate was removed by mass surgery and sent to the pathology laboratory. The prostate was found to be red, sticky, necrotic, and measuring 4 x 7 x 9 cm when viewed macroscopically. Tissue sections prepared after routine tissue processing procedures were stained with Hematoxylin Eosin (HE) and immunohistochemically (IHC) using PCNA antibody. Under a microscope, it was possible to identify acinar/ tubular structures made of atypical tumor cells with or without many central lumens. It was realized that certain tumor cells had vacuoles in their cytoplasm and displayed squamous differentiation. Tumor cells with localized intracytoplasmic eosinophilic bodies (Melamed-Wolinska) were also detected. In some parts of the tumor, epithelial cells embedded in the stroma were seen in the form of “signet ring”. In the immunohistochemical staining of prostate sections with PCNA antibody, severe immunoreactivity was observed in tumor cells. As a result of all these, a rare diagnosis of acinar type prostate adenocarcinoma with urogenital differentiation was made.