Disease of the prostate is relatively common in the intact male dog. Clinical signs including inappropriate urination, tenesmus, and caudal abdominal pain are indicative of prostatic disease. There are four main differentials for disease of the prostate; benign prostatic hyperplasia (BPH), prostatic cysts, prostatic neoplasia, and prostatitis. There is considerable overlap in signs of these diseases, and tools such as radiography, ultrasonography, and cytology are necessary for differentiation. Collection of prostatic fluid for cytology can be accomplished in several ways, including ejaculation, prostatic wash, fine-needle aspiration, and biopsy. Appropriate therapy is dependent on accurate diagnosis of disease, and in the case of bacterial prostatitis includes both castration and appropriate antibiotic therapy. Disease of the prostate can range from asymptomatic and benign to aggressive and life-threatening, and any time disease of the prostate is suspected, further work up is recommended.