The usual histological techniques are necessary and sufficient for the routine diagnosis of bladder tumours. Many laboratory tools are designed to determine prognostic factors but require such technical conditions that they cannot be used routinely. The determination of DNA ploidy by flow cytometry of voided urine, fresh, formalin-fixed or paraffin-embedded tumour fragments is a simple, standardised and reproducible technique and the method of choice of pathologists as it allows morphological control of the element analysed. Based on a series of 720 bladder tumours collected by 3 different centres, the authors demonstrate how to use, correlate and integrate into routine practice the data of image analysis flow cytometry in relation to conventional cytology and histology. 5% of grade 1 tumours, 27% of grade 2 tumours, and 92% of grade 3 tumours were DNA aneuploid. 17% of non-invasive tumours (PTa) and 79% of invasive tumours (PT1 and more) were DNA aneuploid. These proportions are in line with the results of various series in the literature. DNA ploidy is therefore an objective and measurable element completing histological grading. The determination of DNA ploidy also helps the cytologist in difficult cases of urine cytology.