Koichi Sugimoto, Shogo Adomi, Hiroyuki Koike, Atsunobu Esa Department of Urology, NTT West Osaka Hospital, Osaka, Japan Background: Procalcitonin has been advocated as a marker of bacterial infection, so this study was carried out to determine the usefulness of serum procalcitonin in the early diagnosis of urosepsis. Methods: The subjects were 37 febrile patients with urinary tract infection in whom we examined the serum procalcitonin concentration at the start of treatment. Results: Thirty patients had acute pyelonephritis (16 simple, 14 complex), one had emphysematous pyelonephritis, five had acute prostatitis, and one had acute epididymitis. The procalcitonin level was <0.5 ng/mL in 18 patients, ≥0.5 ng/mL in one patient, ≥2 ng/mL in seven patients, and ≥10 ng/mL in 11 patients. Five of the 11 patients with procalcitonin levels ≥ 10 ng/mL had disseminated intravascular coagulation. All patients with urinary tract obstruction and disseminated intravascular coagulation had procalcitonin levels ≥ 10 ng/mL. Conclusion: Although this retrospective study comprised a small number of patients, we found that procalcitonin was a useful marker for urinary tract infection. Keywords: procalcitonin, urosepsis, urinary tract infection, urology