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.The subjects were 37 febrile patients with urinary tract infection in whom we examined the serum procalcitonin concentration at the start of treatment.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.Although this retrospective study comprised a small number of patients, we found that procalcitonin was a useful marker for urinary tract infection.