Reliability of urinary cytology was studied in 678 cases in the pathology department of the A.C. Camargo Hospital from 1966 to 1988. Cytologic diagnosis was compared to the final diagnosis of the patients (histopathologic diagnoses, cystoscopy, and clinical data). The rate of sensitivity, specificity, predictive value (positive and negative), and efficiency was obtained. Patients ranged from 2 months to 88 years, mean age being 59.9, among 446 men and 180 women. Cytologic diagnoses produced 139 positive cases (20.5%), 459 negative (67.7%), 21 "suspected" (3.0%), and 59 unsatisfactory cases (8.8%). There were 306 true negative cases (58.4%), 88 false-negative (16.8%), 126 true-positive (24.0%), and only 4 false-positive (.76%). The authors did not prepare a statistical correlation for the "suspected" and unsatisfactory cases; in 74 cases there was not information enough to perform the necessary comparison. The rate of sensitivity was 59.0%, specificity 98.7%, predictive positive value 96.9%, predictive negative value 77.6%, and efficiency 82.4%.