Acute bacterial prostatitis is a common and clinically important genitourinary disorder. Patient populations who are at especially high risk of acute prostatitis include those with diabetes, cirrhosis, and suppressed immune systems. The cause is usually an ascending infection, but bacteria can also be introduced during transrectal prostate biopsy. Clinical presentation ranges from mild lower urinary tract symptoms to full sepsis. The causative organisms are usually similar to those that cause other common genitourinary infections, and include Escherichia coli and Enterococcus spp. Oral or intravenous antibiotics are usually effective for curing the infection and progression to chronic bacterial prostatitis is, therefore, uncommon. Immunosuppressed patients require special consideration, as bacterial prostatitis in these patients can be caused by atypical infecting organisms and might, therefore, require additional therapies. A lack of response to standard therapy can lead to complications such as a prostatic abscess or fistula.