Common canine prostatic disorders include benign prostatic hypertrophy (BPH), prostatitis, prostatic cysts and prostatic adenocarcinoma. BPH is a spontaneous and age-related disorder of intact male dogs, which occurs in more than 80% male dogs over 5 years of age, and which is associated with clinical signs of sanguinous prostatic fluid, constipation and dysuria. BPH signs respond to castration or to finasteride treatment (0.1-0.5 mg/kg per os once daily), as finasteride inhibits conversion of testosterone to dihydrotestosterone, causing prostatic involution via apoptosis. BPH often occurs concurrently with prostatic infection, abscessation, cysts and neoplasia in the intact dog, and finasteride-induced prostatic involution may be beneficial in treatment of all of these conditions except neoplasia. Two studies suggest that risk of prostatic adenocarcinoma is increased in neutered, compared to intact male dogs. Although canine prostatic neoplasia, unlike human prostatic neoplasia, usually does not respond to androgen deprivation, recent reports of prostatic intraepithelial neoplasia (PIN) in a high percentage of older male dogs, with and without prostatic adenocarcinoma, suggests that PIN may be a precursor to adenocarcinoma in the dog as it is believed to be in man.