Bacterial prostatitis is a common prostate disease in sexually intact male dogs and may be seen in intact male cats. It can develop as an acutely fulminating systemic disorder or, most commonly, as a chronic problem associated with recurrent UTIs. Care should be taken when rectally palpating an acutely infected prostate, because septicemia/endotoxemia can occur. Most, if not all, sexually intact male dogs with UTI also have infectious prostatitis. The prostate gland is uniquely different from the rest of the urinary tract because of the acidity of the prostate glands, leading to a decreasing pH gradient from the blood through the tissue to the acinar glands. The distribution of antimicrobials in the prostatic tissue as well as in the prostatic secretions depends completely on the local pH (6.4) and the pKa of the drugs. For alkaline drugs, a high degree of ionic trapping leads to high antimicrobial concentrations in the tissue and secretions, whereas the acidic drugs such as the β-lactam antimicrobials do not reach concentrations equivalent to plasma concentrations. The choice of antimicrobial for treatment should be based on culture and susceptibility results, and on the ability of the drug to penetrate the blood-prostate barrier. Ideal antimicrobials should be very lipid-soluble, basic, and not highly protein-bound. Fluoroquinolones are the best empirical choice for E coli infections, whereas chloramphenicol, doxycycline, or trimethoprim-sulfas can otherwise be considered with favorable culture and susceptibility results. Antimicrobial therapy may need to be continued for up to 2 mo, which may promote emergence of antimicrobial resistance. Chronic bacterial prostatitis may be difficult to cure. Neutering the dog may increase the likelihood of successful therapy and prevent recurrence.