Emphysematous prostatic abscess is a very rare form of prostatitis. Emphysematous prostatic abscess due to Klebsiella pneumoniae may have a poor prognosis according to a few previous reports. We report a rare case of successfully treated emphysematous prostatic abscess with cystitis due to Klebsiella pneumoniae in a 50-yr-old man with 15-yr history of diabetes mellitus. The patient was referred to the emergency room of our hospital. The KUB film revealed gas shadows in the lower pelvic area suggestive of emphysematous cystitis or emphysematous prostatic abscess. The gas was mainly occupying the prostate and was also seen in the bladder on pelvic CT. The patient was successfully treated with long-term antibiotic use and additional percutaneous drainage of the abscess. Emphysematous prostatic abscess may be misdiagnosed as emphysematous cystitis due to the similar location of gas shadows on radiography. Computerized tomography and transrectal ultrasonography are helpful in making the diagnosis of emphysematous prostatic abscess. Appropriate use of effective antibiotics with drainage of pus is the best treatment. This case emphasizes the importance of timely and accurate diagnosis followed by appropriate treatment in emphysematous prostatic abscess in diabetic patients.