The sensitivity and specificity of urinary cytology in the detection of urothelial tumours using voided urine and applying simple smear preparation and staining techniques have been assessed. Of the 2704 patients under investigation 207 had urothelial tumours. The first urine analysis was positive in 66% of the patients with urothelial carcinoma; an additional 23% of the patients showed positive cytology in repeat smears, resulting in a sensitivity of 89%. The efficacy of urinary cytology depends on the tumour type: for grade 2 tumours, 79% were cytologically positive, 92% of grade 3 and 98% of the grade 4 tumours. The diagnostic efficacy in cases of carcinoma-in-situ, squamous cell carcinoma and adenocarcinoma was comparable with that of grade 4 carcinomas. Grade 0-1 tumours did not result in positive cytology. In eleven cases of lithiasis and in two cases of cyclophosphamide therapy the cytological diagnosis was positive but no neoplasm could be established histologically; these represent true false positive diagnoses. Thus, the false positive rate, 13 out of 165, was 7.88% and the false negative rate, 61 out of 207, was 29.4% when grades 0-1 were included, but 8.75% (14 our of 160) when grades 0-1 were excluded.