The cytologic findings in the urinary sediment of 13 patients with tuberculosis (TB) of the bladder were compared with the histologic findings. TB was cytologically recognized in 11 patients because of the presence of epithelioid and/or Langhans' giant cells. The morphologic deviations of the urothelial cells and the urothelium were classified according to the criteria of Koss. The type I atypical urothelial cells found in ten patients were correlated to the urothelial hyperplasia found at histology; the follow-up data documented the benign reversible nature of the urothelial hyperplasia as the focal expression of the reactive potential of urothelium to various forms of inflammatory processes. The presence of type II atypical urothelial cells reflected moderate and severe atypia of the urothelium at biopsy. In order to assess the reactive, reversible or precancerous nature of these forms of atypia associated with TB, an accurate follow-up is necessary. Since TB of the bladder may cause the presence of atypical cells in the urine, this lesion is of special interest in the differential diagnosis between inflammatory processes and carcinoma.