The authors have investigated the cyto-histologic correlation in 146 patients with primary urinary bladder tumours, and the causes which favor the false negative results. The authors found malignant cells in 92% of all cases, and stress the optimal conditions for the cytological investigation. It is considered that the study of the urinary sediment could replace successfully urinary bladder washing for the cytological surveillance of the patients operated for urinary bladder tumours. Diagnostic difficulties are presented, and the causes of the false negative results, which include: associated affections, special pathological conditions, therapeutical procedures, and technical details. The importance is discussed, of the urinary cytology study for the application of the associated immunostimulating therapy. On the basis of their personal experience the authors present succinctly the indications of urinary cytodiagnosis.