OBJECTIVE To investigate the value of Tc-99m ciprofloxacin imaging in the differential diagnosis of chronic bacterial prostatitis. METHODS The study included 4 normal subjects as the negative controls, 2 patients with acute prostatitis or cystourethritis as the positive controls and 59 patients diagnosed as chronic bacterial prostatitis or chronic pelvic pain syndrome by traditional laboratory tests. In every subject, the single photon emission computerized tomography images were obtained 3 h after intravenous injection of Tc-99m Ciprofloxacin. The results of the imaging were compared with those of laboratory tests. RESULTS On the images, negative uptake was observed in all normal subjects, while strong hot uptake, in the whole prostate of acute prostatitis patients and in the whole urethra of acute cystourethritis patients. In 13 (68%) of 19 patients categorized as chronic bacterial prostatitis by standard laboratory tests, hot uptake with less intensity than that of acute prostatitis was observed in the prostate area around the prostatic urethra. Negative uptake in the prostate was observed in 6 of 19 patients (32%) categorized as chronic bacterial prostatitis. Interestingly, hot uptake in the prostate was exhibited in 28 (70%) of the 40 patients categorized as chronic pelvic pain syndrome. CONCLUSIONS Tc-99m ciprofloxacin imaging is helpful in the differential diagnosis of prostatitis syndrome.